title: Angular2+ memory leaks while using Subscribers and subscribe.first()
body: <p>Im working with an Angular2 app which is run via electron.
  Currently I'm looking to improve performance for the app and reduce memory leaks. I understand that you need to destroy subscribers when the app is destroyed to prevent them watching for new values. But do you need to destroy a subscription which runs only once?</p>
  
  <pre><code>ObservableVar.subscribe().first((ans) =&gt; { // Wanting to use only one ans
      dostuff(ans);
  }
  </code></pre>