Why we use AJAX and why is it so useful for a web developer ?

Ajax has the following key features which makes it so powerful

1- Asynchronous communication between server n client

2- bosst web app speed due to partial postbacks rather then full post backs to server

3- Efficient use of bandwidth (though the differnece can be small but it does impact when you have bigger userbase)

Ajax is mainly required to display new records without refreshing the page..