onSucess = the device has managed to register on the service. It's a one time info, but priceless if we are still struggling to figure out  how to make the whole thing work. For the end user, no that has no use.

About the simplification:  130000% agree :)

About the sound: useless, if we want to make it ring,  don't need the push notification API to do it. The badge (I even don't know what those values - 1, 3, 7... - mean, not yet...)