Read original post by Jonathan Lyons at Windows Phone Developer Blog
Phone apps need to be designed and developed to manage a variety of different conditions that are common in daily life, such as changing network conditions, intermittent network failures, and unexpected phone interruptions. Building and testing apps under lab conditions does not ensure that they will behave well in real-life conditions or handle unexpected user behavior appropriately. There can be many problems which the apps face in real life, such as:
· Crashes due to unhandled network interruptions in flow of data
· Unresponsiveness due to large downloads over slow networks
· Media playback jitters on high-latency networks
· Games continuing in background unaware of a phone call received by user