Ajax is very useful for when you want todo something without refreshing the page plus it’s the way things are done now.
For my Banner Bar program i allow the user to upload images or insert links to images which while this is good i think at the moment it looks confusing and the page is refreshed each time an image is uploaded.
So when looking to improve on this for the next Version of Banner Bar i turned to Ajax after playing with XMLHttpRequests. So now the user can choose to upload an image or insert a link and the form when submitted posts either ‘insert’ or ‘upload’ to the ‘update.php’. Then the Ajax script gets what is sent back and updates the ‘iType’ div innerHTML with what was sent back all without ever refreshing the page!
The above is just a example of what can be done but you would normally use JQuery to hide and show the input fields.
I use something similar to the above to toggle pause for the banners and to upload images.