It enables a web page to participate in partial-page updates without writing any client script.
Moreover, when you use an Update Panel control, the page behavior is browser independent and can potentially reduce the amount of data that is transferred between client and server.
I now see that if I had thought enough about the differences between config options, properties and methods I would not have had to post.
Here Mudassar Ahmed Khan has provided solution with an example and attached sample code for a much known problem these days i.e.
When partial-page updates are enabled, controls can asynchronously post to the server.
An asynchronous postback behaves like a regular postback in that the resulting server page executes the complete page and control life cycle.
But, The problem may come when we want to update the controls which are outside of Update Panel and we need to update the same while updating then control inside updatepanel. Now, our requirement is to update the Label2 while we are updating Label1 by Clicking Button1.
Lable1 present inside the update Panle and Label2 is in the outside of update Panel.