When is it appropriate to use synchronous ajax?

Question

I was just reading another question about jQuery's synchronous ajax call, and I got to wondering:

What circumstances make a synchronous version of an ajax call beneficial/necessary?

Ideally I'd like an example, and why synchronous is better than standard ajax.

Answer 1

The only reasonable example I can think of (that can't be worked around another way) is making a call in window.onbeforeunload, where you need it to be synchronous, or the page will move on and the request will never complete.

In this specific case using standard/asynchronous behavior, you're all but assured the request will die too early to have any impact, or ever contact the server.

I'm not saying I'm in favor of doing this, quite the opposite (as it negatively impacts the user's browsing speed). But...there's not much option here.