Web based applications have completely revolutionized the way an enterprise is automated. Earlier desktop based applications ruled the roost residing on the powerful machines connected to each other, following the client server architecture. But with the advent and advancement of web based technologies, it became possible to bundle up the entire application on the internet, which made those applications easily accessible to every user, irrespective of where they are located. For the IT professionals, it became a lot easier to maintain those applications without having to visit various locations, where the applications are running.
If you look at all the prominent web based applications today, especially those which most of us use regularly like Google and Facebook are full of state of the art features created using AJAX. You will never find an awkward flicker of any sorts anywhere. So if you are planning to pursue a career in web technologies, learning AJAX should be among your top priorities.