For three different pages I measured the size of the HTML sent to the browser (excluding images and CSS).
What I found was:
A page that has normal ASP.NET controls + a little bit of jQuery: approx. size = 30kb
A page using some user controls that have AJAX and client side support: approx size = 50kb
A page that uses more complex user controls from a library with heavy client side support: approx. size = 110kb
As you can see the size of data transferred seems to increase as client side support and AJAX features are added.
This adds to the bandwidth requirements of the site and presumably the servers I/O load which may reduce the number of concurrent users that can be served.
Should I worry about balancing rich client side features and interactivity with server's load and bandwidth use?
What are the priorities, if any?