We pull data from server, and for that, If we are using Struts, then we can pull either by submitting a page, which is MVC Architecture or we can make an AJAX call, but conventions is of using forms and render a response, but we also face challenges to give rich user experience, so we compromise convention and start using excessive AJAX, so how we should make balance between two?
I personally think that AJAX should be used for displays updates and form submissions should be done via a page reload. Reasoning?
When submitting forms, you are telling the application to do something. Users tend to want to feel that it was done. When a page doesn't reload, users are often left wondering "Did that work?". Then they have to check to make sure what they did was right.
On the other hand, when you are displaying a chart or something, and the user says to "display 2011 data....now 2012 data" for instance, they aren't "doing" something (creating new entities, sending emails, etc). So AJAX can provide a nice user interface in this case. Page reloads would be annoying here.
In conclusion, I think form submission should be done via page reloads (let the user see it working), whereas display updates should use AJAX (prevent annoying page reloads).
Of course, this is a preference thing. Some of my company's applications use AJAX all over. But those are the applications that are the most difficult to maintain and debug. ;)