title: In Slick 3.0, why is the newly-introduced `Streaming` useful?
body: <p>I found Slick 3.0 introduced a new feature called <code>streaming</code></p>
  
  <p><a href="http://slick.typesafe.com/doc/3.0.0-RC1/database.html#streaming">http://slick.typesafe.com/doc/3.0.0-RC1/database.html#streaming</a></p>
  
  <p>I'm not familiar with Akka. <code>streaming</code> seems a lazy or async value, but it is not very clear for me to understand why it is useful, and when will it be useful..</p>
  
  <p>Does anyone have ideas about this?</p>