user-1: lets say.
i have created a raw transaction with inputs = outputs aka setting 0 fees.
so when i do 
bitcoin-cli sendrawtransaction <signed_hex> 1

1 is for allowhighfees 
what it actually does ?
if it increases fees ? then how much ? 
how much fees does it sets per byte ?
What if there is not much satoshis in input to cover the fees ?

user5757: The fee is whatever you define in the raw transaction, based on the difference between inputs and outputs.  sendrawtransaction never changes it.  However, as a safety measure, it will normally reject your transaction if the fee exceeds a certain "absurd" threshold, so that you don't accidentally lose a lot of coins by miscalculating your raw transaction.  If you set the allowhighfees parameter, this check is disabled, and you can send a transaction with fees as high as you wish.
The threshold value can be set with the maxtxfee command line / config file option.

-1: <p>lets say.</p>

<p>i have created a raw transaction with <code>inputs = outputs</code> aka setting <code>0 fees</code>.</p>

<p>so when i do </p>

<pre><code>bitcoin-cli sendrawtransaction &lt;signed_hex&gt; 1
</code></pre>

<p><code>1</code> is for <code>allowhighfees</code> </p>

<p>what it actually does ?
if it increases fees ? then how much ? </p>

<p>how much fees does it sets per byte ?</p>

<p>What if there is not much satoshis in input to cover the fees ?</p>
 5757: <p>The fee is whatever you define in the raw transaction, based on the difference between inputs and outputs.  <code>sendrawtransaction</code> never changes it.  However, as a safety measure, it will normally reject your transaction if the fee exceeds a certain "absurd" threshold, so that you don't accidentally lose a lot of coins by miscalculating your raw transaction.  If you set the <code>allowhighfees</code> parameter, this check is disabled, and you can send a transaction with fees as high as you wish.</p>

<p>The threshold value can be set with the <code>maxtxfee</code> command line / config file option.</p>
