When is it appropriate to use AJAX?

Question

When is it appropriate to use AJAX?
what are the pros and cons of using AJAX?

In response to my last question: some people seemed very adamant that I should only

Answer 1

AJAX is usually used to perform an HTTP request while the page is already loaded (without loading another page).

The most common use is to update part of the view. Note that this does not include refreshing the whole view since you could just navigate to a new page.

Another common use is to submit forms. In all cases, but especially for forms, it is important to have good ways of handling browsers that do not have javascript or where it is disabled.

Answer 2

When your application (or your users) demand a richer user experience than a traditional webpage is able to provide.