That introduces a noticeable delay. It's acceptable in some situations but in others less so. Having immediate feedback on button press or text entry makes the UX much more pleasant.
This is still rather easy. You can change the UI (i.e. set the button into a "Loading..." state) directly after the click and when the server sends back the response act accordingly. An error would reset the button and prompt an error message.
Exactly. The difference is, this becomes the default behavior (minus the spinner), and simple to implement.
With rest, it would be a much more manually implemented feature. The default would be to just fail silently and potentially drop important data on the next page load.
