[Brad]

Originally Posted by Zero Tolerance

You'll notice the one and only passive variable here for the function 'vB_AJAX_Handler' is set to 'true', this determines wether to use asynchronous or not, set to false if you do not desire to use it, if you're unsure leave this set to true.

Just to add to this:

Asynchronously:

Processing is done in the backround and allows the user to use do other things on the page while the request is begin made and returned. You should use this is most cases

Synchronously:

Page is 'locked' until request is made and data is returned to the browser. This should not be used often because if there is a connection timeout or other issues the user will be left with a page that will not function.