This is a quick benchmark to demonstrate the potential performance gain of using jQuery.deferred() in conjunction with AJAX calls, over the traditional nested AJAX. Each test uses two AJAX calls. The first test runs the two calls in parallel (deferred), and the second test in sequence (nested). They both use the same AJAX callback, which is a simple PHP script that has a 1s delay, then returns a random number.
Parallel:
Sequence: