Each of the preceding modes lets the system know that your app should be woken up or launched at appropriate times to respond to relevant events. For example, an app that begins playing music and then moves to the background still needs execution time to fill the audio output buffers. Enabling the Audio mode tells the system frameworks that they should continue to make the necessary callbacks to the app at appropriate intervals. If the app does not select this mode, any audio being played or recorded by the app stops when the app moves to the background.