Yes, integrating with Ad Networks affects App's Performance a bit. In Fact the Majority of the Crash counts in your crash report would be because of the Ad not Received Operation. The more you use App the more async tasks carry out and the phone CPU cycles are required to perform simultaneous functions. The Reason that App works smoother on Emulator is that the Emulator has free RAM and no background tasks of other Apps besides your App if it has any. This can be considered as the most Ideal condition that may not reflect practically in windowsphone and depends on the number of Apps, available memory, etc. in an individual windowsphone