First time page load is heavy, yes. Then after that, it's much faster, as all the server has to hand over is JSON, which can turn a 150-500ms page load to a 15-

First time page load is heavy, yes. Then after that, it's much faster, as all the server has to hand over is JSON, which can turn a 150-500ms page load to a 15-90ms page load. Furthermore, it allows for easier data portability- when you can 'collect' data as you go and have API calls that much faster, it's okay to make more expressive UI decisions. Not to mention, at the end of the day I like having a separation between my frontend and backend. Frontend testing from Rails or Django always feels a little dirty, a little off, and in many cases is even a discouraged practice("If you need to test your view, you should be using a helper" logic). I also like not ever having to make model method choices based on what my frontend desires might be- the concerns can be completely separate. And lastly, I frankly can do a lot more interesting things much faster in Ember than I can in Rails from a UI standpoint. Ember turned my favorite part of software development, UI design, into the joy it used to be when I was just using pad and paper.