Think of Ember controllers as proxies, or pointers if you will. The idea is you can have a commentsController instance, and when you switch to a different post

Think of Ember controllers as proxies, or pointers if you will. The idea is you can have a commentsController instance, and when you switch to a different post, the view(s) bound to it will automatically pick up the new comments array that is swapped out on behind the controller. Routing is just rewiring the pointers on your controllers and getting the right views up on the page.