The beauty of it is that because the AJaX engine is handling the requests, it can hold most information in the engine itself, while allowing the interaction with the application and the customer to happen asynchronously and independently of any interaction with the server.
asynchronously loads graphic tiles to support map scrolling
Google Suggest – http://www.google.com/suggest
asynchronously updates list of possible topic matches based on what has been typed so far
even when there is nothing useful for the user to do after a request is submitted to a server, AJaX can be used to retrieve data and update selected parts of the page without refreshing the entire page
Due to the fact that Ajax applications are mostly executed on the user's computer, they can perform a number of tasks without their performance being limited by the network. This permits the development of interactive applications, in particular reactive and rich graphic user interfaces.
Ajax applications target a (relatively) well-documented platform, implemented by all major browsers on most existing platforms. Ajax applications are effectively cross-platform.
While the Ajax platform is more restricted than the Java platform, current Ajax applications effectively fill part of the one-time niche of Java applets: extending the browser with portable, lightweight mini-applications.
Users generally expect that clicking the back button in web applications will undo their last change and in Ajax applications this might not be the case.
The interval between user request and server response — needs to be considered carefully during Ajax development. Without clear feedback to the user, the users might experience delay in the interface of the web application.