user7039: There is a part of Yuttadhammo's answer at 
How to practice Metta without a Benefactor? 
that has very confused me:

cultivate metta towards yourself (useless, but a good example)

Why is metta useless? 
Are there any specific sources for this statement, or is this based on a determine school?

user-1: Householder Louis, interested,
as one stated in an answer, such a statement comes often from those actually having Nihilist Views. This monk, by such a statement, not only disregard the elders, but also the Buddha and his teachings.
Next to the fact that all traditional followers start practicing metta with having such for themselfs, a matter of right view, even the Karaṇīya Metta-Sutta starts with metta, goodwill toward oneself.

Karaṇīyam'atthakusalena, yaŋ taŋ santaŋ padaŋ abhisamecca:
He who is skillful in his welfare, 
  and wishes to attain that state of Peace should act thus:...

So the drive is actually metta toward oneself. One doesn't have goodwill toward himself is never able to practice toward and on the path.
It's good not to stick much to "western/modern" ideas, since for the most they come from a Nihilist background, (previously) follower of other sects.
Note that many are disciples of this modern sect leaders here and reflect similar Nihilist and Jain-Uposatha approaches.
For mor an the topic see previous answer on: How to view people with metta and karuna?
Also Buddhadasa is one of this modern Sect leader, with same approaches like the young Canadian monk:
Does this statement by Buddhadasa Bhikkhu conflict with traditional mettā meditation?

Sakko ujū ca sūjū ca (being honest, very honest: a very prerequisite, not only for metta practice with conductive effects)
The Buddhas words on one occation: "Do you really love yourself? Are you going to content yourself simply with the food, clothing, shelter, and medicine of lay life even though this means staying in the cycle of birth, aging, illness, and death? Or would you really like to put an end to suffering?" (See: "Selves & Not-self", by Ven. Thanissaro on more about general instances on the roots here)

Metta toward what is dear and near, starting by really having goodwill toward one self, is right effort, is the foundation, when added samvega, for the path and the only way not developing something harmful for oneself and others, even when the four noble truth are not developed. Other kinds of metta will be hypocritical, void of virtue, void of path toward Brahma-Vihara, access and path. Even King and Queen realiced that by themselves:

...“That's the way it is, great king! That's the way it is! Those who engage in bodily misconduct, verbal misconduct, & mental misconduct are not dear to themselves. Even though they may say, 'We are dear to ourselves,' still they aren't dear to themselves. Why is that? Of their own accord, they act toward themselves as an enemy would act toward an enemy; thus they aren't dear to themselves. But those who engage in good bodily conduct, good verbal conduct, & good mental conduct are dear to themselves. Even though they may say, 'We aren't dear to ourselves,' still they are dear to themselves. Why is that? Of their own accord, they act toward themselves as a dear one would act toward a dear one; thus they are dear to themselves.”
That is what the Blessed One said. Having said that, the One Well-Gone, the Teacher, said further:
If you hold yourself dear
  then don't fetter yourself
          with evil,
  for happiness isn't easily gained
      by one who commits
      a wrong-doing.
When seized by the End-maker
      as you abandon the human state,
  what's truly your own?
  What do you take along when you go?
  What follows behind you
      like a shadow
      that never leaves?
Both the merit & evil
      that you as a mortal
      perform here:
  that's      what's truly your own,
          what you take along when you go;
  that's      what follows behind you
      like a shadow
      that never leaves.
So do what is admirable,
  as an accumulation
      for the future life.
  Deeds of merit are the support for beings
      when they arise
      in the other world.
Piya Sutta

One rejecting that he is worthy to have goodwill with himselves, would not fear to harm himself and break his virtue. Those who act like fools often say "I accept hell for the well-fare of (some) other" or act "Jesus-like" and in foolish hero-ways.

Searching all directions
  with your awareness,
  you find no one dearer
      than yourself.
  In the same way, others
  are thickly dear to themselves.
  So you shouldn't hurt others
      if you love yourself.
Rājan Sutta

The Buddha himself started his journey being dear to himself and all real warriors would follow in this way. A nice ballad has been written by one of them, reflecting the way "ex-bodhisattas" start to walk the path:

The Ballad of Liberation from the Khandhas
...Once there was a man who loved himself
  and feared distress. He wanted happiness
  beyond the reach of danger, so he wandered
  endlessly. Wherever people said
  that happiness was found, he longed to go,
  but wandering took a long, long time.
  He was the sort of man who loved himself
  and really dreaded death. He truly wanted
  release from aging & mortality.
  Then one day he came to know the truth,
  abandoning the cause of suffering &
  compounded things. He found a cave of wonders,
  of endless happiness, i.e., the body.

An at least, every developing of metta, Brahma-Viharas, in the good old tradition of the noble ones starts with oneself:

Ahaṃ sukhito homi
  May I be happy.
Niddukkho homi
  May I be free from stress & pain.
Avero homi
  May I be free from animosity.
Abyāpajjho homi
  May I be free from oppression.
Anīgho homi
  May I be free from trouble.
Sukhī attānaṃ pariharāmi
  May I look after myself with ease.
(METTĀ — GOOD WILL)
  Sabbe sattā sukhitā hontu.
  May all living beings be happy...

As long as one does not understand that what ever, good or bad, one does for oneself and beyond, no developing of right view and path can be expected. It's because beings do either not hold them dear or don't know the way to long lasting happiness, harming themselves in many, even perverse ways, that they being do not even master the way toward the Brahmas, or any Jhana, path or fruit.
What does no like to give and share not even made his at first place?
(Note that this gift of Dhamma is not dedicated for trade, exchange, stacks or entertainment but as a means to make merits toward release from this wheel)

user295: I think this needs qualification. 
Metta towards oneself helps reduce self hate. So this is not completely useless. Also this is the basis of developing Metta to others. If you do not love yourself you cannot love others. [page 83 Knowing and Seeing - 4th Edition by Ven Pa-Auk Sayadaw]
You cannot attain Jhana if the person is oneself, hence as a means to achieve Jhana this is useless. [page 82 Knowing and Seeing - 4th Edition by Ven Pa-Auk Sayadaw]
Other objectives is as an antidote to hateful temperament towards others. On this perspective this is useless if you contemplate about only oneself and not of others, but useful if you contemplate about oneself and others. As you cannot love others if you do not love yourself hence oneself should be included.
Also this is used to break barriers [page 85 Knowing and Seeing - 4th Edition by Ven Pa-Auk Sayadaw] as perceiving someone dear, neutral and foe. In this perspective it is useful to asses the level of love to oneself vs loved one vs neutral people vs foes, but not useful if you contemplate only about oneself and not others, and only others and not oneself, and useful when you contemplate on oneself and others.

7039: <p>There is a part of Yuttadhammo's answer at </p>

<p><a href="https://buddhism.stackexchange.com/questions/7865/how-to-practice-metta-without-a-benefactor?rq=1">How to practice Metta without a Benefactor?</a> </p>

<p>that has very confused me:</p>

<blockquote>
  <p>cultivate metta towards yourself <strong>(useless, but a good example)</strong></p>
</blockquote>

<p>Why is metta useless? </p>

<p>Are there any specific sources for this statement, or is this based on a determine school?</p>
 -1: <p>Householder Louis, interested,</p>

<p>as one stated in an answer, such a statement comes often from those actually having Nihilist Views. This monk, by such a statement, not only disregard the elders, but also the Buddha and his teachings.</p>

<p>Next to the fact that all traditional followers start practicing metta with having such for themselfs, a matter of right view, even the <a href="http://zugangzureinsicht.org/html/lib/authors/nanadassana/metta_en.html" rel="nofollow noreferrer">Karaṇīya Metta-Sutta</a> starts with metta, goodwill toward oneself.</p>

<blockquote>
  <p><em>Karaṇīyam'atthakusalena, yaŋ taŋ santaŋ padaŋ abhisamecca:</em></p>
  
  <p><strong>He who is skillful in his welfare, 
  and wishes to attain that state of Peace</strong> should act thus:...</p>
</blockquote>

<p>So the drive is actually metta toward oneself. One doesn't have goodwill toward himself is never able to practice toward and on the path.</p>

<p>It's good not to stick much to "western/modern" ideas, since for the most they come from a Nihilist background, (previously) follower of other sects.</p>

<p>Note that many are disciples of this modern sect leaders here and reflect similar Nihilist and Jain-Uposatha approaches.</p>

<p>For mor an the topic see previous answer on: <a href="https://buddhism.stackexchange.com/a/24628/11235">How to view people with metta and karuna?</a></p>

<p>Also Buddhadasa is one of this modern Sect leader, with same approaches like the young Canadian monk:</p>

<p><a href="https://buddhism.stackexchange.com/a/25016/11235">Does this statement by Buddhadasa Bhikkhu conflict with traditional mettā meditation?</a></p>

<blockquote>
  <p>Sakko ujū ca sūjū ca (being honest, very honest: a very prerequisite, not only for metta practice with conductive effects)</p>
  
  <p>The Buddhas words on one occation: "Do you really love yourself? Are you going to content yourself simply with the food, clothing, shelter, and medicine of lay life even though this means staying in the cycle of birth, aging, illness, and death? Or would you really like to put an end to suffering?" (See: "Selves &amp; Not-self", by Ven. Thanissaro on more about general instances on the roots here)</p>
</blockquote>

<p>Metta toward what is dear and near, starting by really having goodwill toward one self, is right effort, is the foundation, when added samvega, for the path and the only way not developing something harmful for oneself and others, even when the four noble truth are not developed. Other kinds of metta will be hypocritical, void of virtue, void of path toward Brahma-Vihara, access and path. Even King and Queen realiced that by themselves:</p>

<blockquote>
  <p>...“That's the way it is, great king! That's the way it is! Those who engage in bodily misconduct, verbal misconduct, &amp; mental misconduct are not dear to themselves. Even though they may say, 'We are dear to ourselves,' still they aren't dear to themselves. Why is that? Of their own accord, they act toward themselves as an enemy would act toward an enemy; thus they aren't dear to themselves. But those who engage in good bodily conduct, good verbal conduct, &amp; good mental conduct are dear to themselves. Even though they may say, 'We aren't dear to ourselves,' still they are dear to themselves. Why is that? Of their own accord, they act toward themselves as a dear one would act toward a dear one; thus they are dear to themselves.”</p>
  
  <p>That is what the Blessed One said. Having said that, the One Well-Gone, the Teacher, said further:</p>
  
  <p><code>If you hold yourself dear
  then don't fetter yourself
          with evil,
  for happiness isn't easily gained
      by one who commits
      a wrong-doing.</code></p>
  
  <p><code>When seized by the End-maker
      as you abandon the human state,
  what's truly your own?
  What do you take along when you go?
  What follows behind you
      like a shadow
      that never leaves?</code></p>
  
  <p><code>Both the merit &amp; evil
      that you as a mortal
      perform here:
  that's      what's truly your own,
          what you take along when you go;
  that's      what follows behind you
      like a shadow
      that never leaves.</code></p>
  
  <p><code>So do what is admirable,
  as an accumulation
      for the future life.
  Deeds of merit are the support for beings
      when they arise
      in the other world.</code></p>
  
  <p><a href="http://accesstoinsight.eu/en/tipitaka/sut/sn/sn03/sn03.004.than" rel="nofollow noreferrer">Piya Sutta</a></p>
</blockquote>

<p>One rejecting that he is worthy to have goodwill with himselves, would not fear to harm himself and break his virtue. Those who act like fools often say "I accept hell for the well-fare of (some) other" or act "Jesus-like" and in foolish hero-ways.</p>

<blockquote>
  <p><code>Searching all directions
  with your awareness,
  you find no one dearer
      than yourself.
  In the same way, others
  are thickly dear to themselves.
  So you shouldn't hurt others
      if you love yourself.</code></p>
  
  <p><a href="http://accesstoinsight.eu/en/tipitaka/sut/kn/ud/ud.5.01.than?" rel="nofollow noreferrer">Rājan Sutta</a></p>
</blockquote>

<p>The Buddha himself started his journey being dear to himself and all real warriors would follow in this way. A nice ballad has been written by one of them, reflecting the way "ex-bodhisattas" start to walk the path:</p>

<blockquote>
  <p><a href="http://zugangzureinsicht.org/html/lib/thai/mun/ballad_en.html" rel="nofollow noreferrer">The Ballad of Liberation from the Khandhas</a></p>
  
  <p>...<code>Once there was a man who loved himself
  and feared distress. He wanted happiness
  beyond the reach of danger, so he wandered
  endlessly. Wherever people said
  that happiness was found, he longed to go,
  but wandering took a long, long time.
  He was the sort of man who loved himself
  and really dreaded death. He truly wanted
  release from aging &amp; mortality.
  Then one day he came to know the truth,
  abandoning the cause of suffering &amp;
  compounded things. He found a cave of wonders,
  of endless happiness, i.e., the body.</code></p>
</blockquote>

<p>An at least, every <a href="http://zugangzureinsicht.org/html/lib/authors/dhammayut/chanting_en.html#sublime" rel="nofollow noreferrer">developing of metta, Brahma-Viharas</a>, in the good old tradition of the noble ones starts with oneself:</p>

<blockquote>
  <p><code>Ahaṃ sukhito homi
  May I be happy.</code></p>
  
  <p><code>Niddukkho homi
  May I be free from stress &amp; pain.</code></p>
  
  <p><code>Avero homi
  May I be free from animosity.</code></p>
  
  <p><code>Abyāpajjho homi
  May I be free from oppression.</code></p>
  
  <p><code>Anīgho homi
  May I be free from trouble.</code></p>
  
  <p><code>Sukhī attānaṃ pariharāmi
  May I look after myself with ease.</code></p>
  
  <p><code>(METTĀ — GOOD WILL)
  Sabbe sattā sukhitā hontu.
  May all living beings be happy...</code></p>
</blockquote>

<p>As long as one does not understand that what ever, good or bad, one does for oneself and beyond, no developing of right view and path can be expected. It's because beings do either not hold them dear or don't know the way to long lasting happiness, harming themselves in many, even perverse ways, that they being do not even master the way toward the Brahmas, or any Jhana, path or fruit.</p>

<p>What does no like to give and share not even made his at first place?</p>

<p><em>(Note that this gift of Dhamma is not dedicated for trade, exchange, stacks or entertainment but as a means to make merits toward release from this wheel)</em></p>
 295: <p>I think this needs qualification. </p>

<p>Metta towards oneself helps reduce self hate. So this is not completely useless. Also this is the basis of developing Metta to others. If you do not love yourself you cannot love others. [page 83 <a href="http://www.dhammatalks.net/Books13/Pa-Auk-Sayadaw_Knowing-and-Seeing-4th-Ed-2010.pdf" rel="noreferrer">Knowing and Seeing - 4th Edition</a> by Ven Pa-Auk Sayadaw]</p>

<p>You cannot attain Jhana if the person is oneself, hence as a means to achieve Jhana this is useless. [page 82 <a href="http://www.dhammatalks.net/Books13/Pa-Auk-Sayadaw_Knowing-and-Seeing-4th-Ed-2010.pdf" rel="noreferrer">Knowing and Seeing - 4th Edition</a> by Ven Pa-Auk Sayadaw]</p>

<p>Other objectives is as an antidote to hateful temperament towards others. On this perspective this is useless if you contemplate about only oneself and not of others, but useful if you contemplate about oneself and others. As you cannot love others if you do not love yourself hence oneself should be included.</p>

<p>Also this is used to break barriers [page 85 <a href="http://www.dhammatalks.net/Books13/Pa-Auk-Sayadaw_Knowing-and-Seeing-4th-Ed-2010.pdf" rel="noreferrer">Knowing and Seeing - 4th Edition</a> by Ven Pa-Auk Sayadaw] as perceiving someone dear, neutral and foe. In this perspective it is useful to asses the level of love to oneself vs loved one vs neutral people vs foes, but not useful if you contemplate only about oneself and not others, and only others and not oneself, and useful when you contemplate on oneself and others.</p>
