title: What is the behavior of scala.concurrent.ExecutionContext.Implicits.global?
body: <p>The documentation for <code>scala.concurrent.ExecutionContext.Implicits.global</code> on the <a href="https://github.com/scala/scala/blob/master/src/library/scala/concurrent/ExecutionContext.scala" rel="noreferrer">ExecutionContext</a> trait reads:</p>
  
  <blockquote>
    <p>It is possible to simply import
    <code>scala.concurrent.ExecutionContext.Implicits.global</code> to obtain an
    implicit <code>ExecutionContext</code>. This global context is a reasonable
    default thread pool</p>
  </blockquote>
  
  <p>What does it mean by "reasonable default"?</p>