title: What is Subject.asObservable good for?
body: <p>Why does RxJava need <code>asObservable</code>?</p>
  
  <p>Technically each Subject is already an Observable. What is the advantage of it over just casting it like</p>
  
  <pre class="lang-java prettyprint-override"><code>Observable obs = subject;
  </code></pre>