This is one of the items that is tested in your Windows 8 App when you use the WACK.
If you are in Southern California, please email this post for more information on getting a token for your app by June 30, 2012!
Even though network operations are asynchronous; optimizing network calls helps with user perception of how responsive (or ready) your application is. Common networking call optimizations you should make include:
Canceling pending network operations when they are not needed. Don’t do work that won’t be used. Design your APIs to return the right amounts of data. If you return too much, you will be executing extra parsing and downloading extra data that might cost the user on a metered network; if you download too little, you will be making too many calls (effectively wasting more bandwidth and leading to longer delays) on data that needs to be readily available for display to the user.