Asp .Net Ajax Timer is useful control to do a repetitive task like constantly viewing current information, auto save etc.
Its event is tick with time interval. So every period of interval time the tick event will be executed.
This Asp .Net Timer control is much like windows form timer control.
I already have post about this Timer control on my previous post, please refer to this Introduction To Asp .Net Ajax 4 (Timer)
One of advantage using Timer is that we code more on server script instead of Js client script. So that we can use Asp .Net server script feature.
But other developers might be more comfortable using client script and then it is more like a choice. Remember that every server side script that update the UI will use server’s resources.
So it is better to consider your code, traffic and related resources.
However, this Asp .Net Timer control is a good option to go and in this post I give you an example to make web chat from scratch using it.
Chat user sees their friend messages by constantly refresh a message board, checking whether there are any new incoming messages or not. Timer is used to do this.