Its no secret that (only) the gridview control have a new property which enables automaticly client callback instead of postback. This works only for sorting and paging.
EnableSortingAndPagingCallbacks
="True" The diffrence is a better UI for the user. But another point is hidden. The amount of traffic.
To measure the traffic, i use fiddler, a great and free http debug proxy from Microsoft. My scenario uses northwind customers and show 10 entrys per page. Task is show page, sort by customerid and sort again by customer id.
Result:
without callback
- 3 times ~9600 Bytes transfered (per request)
with callback
- 1st reqest ~13.000 Bytes
- Webresource ~13.000 Bytes
- Webresource ~ 1400
- 2 times (sort) ~7500 Bytes
So you can see Client Callbacks (also Ajax) does not always reduce the amount of traffic. It depends. In our scenario we have ~30K adverse ~42K which is more then 30 % diffrence.