title: What is the difference between "Future.successful(None)" and "Future(None)"
body: <p><code>Future.apply</code> starts an asynchronous computation whereas <code>Future.successful</code> creates an already completed Future with the specified result.</p>
  
  <p>Now is <code>Future(None)</code> (<code>Future.apply(None)</code>) less efficient than <code>Future.successful(None)</code>?</p>