Use of Ember run loop

I am trying to understand the actual usage of Ember run loop in apps.

So here is what I have observed

Ember has 2 way bindings..So if I update any attribute value in my JS code, the corresponding change should reflect on the UI automatically.

But in some cases, we have to do something like

Ember.run.next Ember.run.scheduleOnce

etc

I wanted to understand in which cases do we need to add the Ember.run.* & in which scenarios do the values not re-render automatically on UI ?