An AJAX-enabled website has three major benefits:
- Less bandwidth use
- More responsive
- More like a desktop application
A normal ASP.Net page does a full postback whenever certain events are triggered, more specifically button Click events. What that means is the state of the whole page is sent to the server, updated, and then the whole page is returned to display to the user.
What AJAX does is allow the webpage to do a postback on small parts of the page. By creating an UpdatePanel, only the part of the page inside of it will postbacked. Thus the rest of the page can remain intact.
The obvious benefit of not having to resend the entire page is the reduced use of bandwidth. Also not having to refresh the entire page makes the ASP.Net page faster and more responsive. Thus behaving more like a desktop application.
The best part of AJAX is that it's super easy to integrate into your webpages. Simply install the Microsoft Atlas Framework and you are good to go. Just remember to add a ScriptManager on the very top of the ASP.Net page.
As you might have guessed by now, AJAX opens up the door to all kinds of custom web controls. Atlas Framework does The not come with : many prebuild controls so a good place to start is with the Ajax Control Toolkit .