emberjs - explain scheduleOnce in this context

I have a nested component and I needed it to rerender on occassion. First of all I tried to simply call the rerender method:

modelUpdated: function() {
  this.rerender();
}

But I got this error message:

You can't use appendChild outside of the rendering process

The solution was to use the run loop but I'm confused as to why this works:

modelUpdated: function(model){
  Ember.run.scheduleOnce('render', this, 'rerender')
}

My understanding of scheduleOnce is that it will create a run loop if one does not exist and I the rerender method will be executed once in the render queue of the runloop.

I'm confused as to why this would go in the render queue and an explanation would be great.