user3919: At the protocol level bitcoins don't actually exists, but rather base units (recently called “satoshis”). Bitcoins are defined as 108 base units, meaning that for a 50 BTC mining reward, you are actually earning 5 000 000 000 units.
So, why was 108 chosen as the value of one bitcoin relative to the base unit?

user63275: The world GDP is $74 trillion footnote: a according to the World Bank in 2017. The max supply of Bitcoin with 108 base units is 2,100 trillion Satoshis.
If Bitcoin is to back the world's money, markets and real estate, not including debt nor derivatives, then the valuation of Bitcoin might be:
Global Stock Markets: $73 trillion
Global Broad Money: $90.4 trillion
Global Real Estate: $217 trillion
Total: $380.4 trillion footnote: b 
With a $380.4 trillion economy and 2,100 trillion satoshis in existence there will be plenty to go around. Additionally, because of the scarcity model built into bitcoin (21 million max supply), we won't need additional bitcoins or more decimal places, the valuation of Bitcoin will naturally change with our economy.
I believe we will use Bitcoin as a form of digital gold to back other digital currencies and online marketplaces, allowing people and businesses to move credits from one online marketplace to another or from one currency to another.
a The $74 Trillion Global Economy in One Chart:
http://www.visualcapitalist.com/74-trillion-global-economy-one-chart/
b All of the World’s Money and Markets in One Visualization:
http://money.visualcapitalist.com/worlds-money-markets-one-visualization-2017/

user3919: When developing Bitcoin, Satoshi had already come with the idea that no more than 21 million of them will ever be made. However, there was an unsolved issue: how to accomodate all bitcoins in case it was actually used as a worldwide currency? Comparing to the current (2008?) world's M1 supply, it was determined that 8 decimal places was enough to cover the supply and still have the smallest division smaller than enough for daily usage.1
It's also worth noting that this decision means the total Bitcoin supply is approximately 250.89, which means it's smaller than the maximum value for a 64-bit integer (263-1), and smaller than the first integer that can't be exactly represented in a double-precision floating-point number (253 + 1), so that standard programming languages can deal with Bitcoin amounts without requiring custom implementations or dealing with overflowing.2

Ray Dillinger's response to: Why 1BTC should equal 10^8 satoshi ?
Satoshi’s Genius: Unexpected Ways in which Bitcoin Dodged Some Cryptographic Bullets


3919: <p>At the protocol level bitcoins don't actually exists, but rather base units (recently called “satoshis”). Bitcoins are defined as 10<sup>8</sup> base units, meaning that for a 50 BTC mining reward, you are actually earning 5 000 000 000 units.</p>

<p>So, why was 10<sup>8</sup> chosen as the value of one bitcoin relative to the base unit?</p>
 63275: <p>The world GDP is $74 trillion <sup>footnote: a</sup> according to the World Bank in 2017. The max supply of Bitcoin with 10<sup>8</sup> base units is 2,100 trillion Satoshis.</p>

<p>If Bitcoin is to back the world's money, markets and real estate, not including debt nor derivatives, then the valuation of Bitcoin might be:</p>

<p>Global Stock Markets: $73 trillion<br>
Global Broad Money: $90.4 trillion<br>
Global Real Estate: $217 trillion<br>
Total: $380.4 trillion <sup>footnote: b</sup> <br></p>

<p>With a $380.4 trillion economy and 2,100 trillion satoshis in existence there will be plenty to go around. Additionally, because of the scarcity model built into bitcoin (21 million max supply), we won't need additional bitcoins or more decimal places, the valuation of Bitcoin will naturally change with our economy.</p>

<p>I believe we will use Bitcoin as a form of digital gold to back other digital currencies and online marketplaces, allowing people and businesses to move credits from one online marketplace to another or from one currency to another.</p>

<p><sup>a</sup> <strong>The $74 Trillion Global Economy in One Chart</strong>:<br>
<a href="http://www.visualcapitalist.com/74-trillion-global-economy-one-chart/" rel="nofollow noreferrer">http://www.visualcapitalist.com/74-trillion-global-economy-one-chart/</a></p>

<p><sup>b</sup>  <strong>All of the World’s Money and Markets in One Visualization</strong>:<br>
<a href="http://money.visualcapitalist.com/worlds-money-markets-one-visualization-2017/" rel="nofollow noreferrer">http://money.visualcapitalist.com/worlds-money-markets-one-visualization-2017/</a></p>
 3919: <p>When developing Bitcoin, Satoshi had already come with the idea that no more than 21 million of them will ever be made. However, there was an unsolved issue: how to accomodate all bitcoins in case it was actually used as a worldwide currency? Comparing to the current (2008?) world's M1 supply, it was determined that 8 decimal places was enough to cover the supply and still have the smallest division smaller than enough for daily usage.<sup><a href="https://bitcointalk.org/index.php?topic=819656.msg9170781#msg9170781">1</a></sup></p>

<p>It's also worth noting that this decision means the total Bitcoin supply is approximately 2<sup>50.89</sup>, which means it's smaller than the maximum value for a 64-bit integer (2<sup>63</sup>-1), and smaller than the first integer that can't be exactly represented in a double-precision floating-point number (2<sup>53</sup> + 1), so that standard programming languages can deal with Bitcoin amounts without requiring custom implementations or dealing with overflowing.<sup><a href="http://bitcoinmagazine.com/7781/satoshis-genius-unexpected-ways-in-which-bitcoin-dodged-some-cryptographic-bullet/">2</a></sup></p>

<ol>
<li><a href="https://bitcointalk.org/index.php?topic=819656.msg9170781#msg9170781">Ray Dillinger's response to: Why 1BTC should equal 10^8 satoshi ?</a></li>
<li><a href="http://bitcoinmagazine.com/7781/satoshis-genius-unexpected-ways-in-which-bitcoin-dodged-some-cryptographic-bullet/">Satoshi’s Genius: Unexpected Ways in which Bitcoin Dodged Some Cryptographic Bullets</a></li>
</ol>
