It's nice to be able to control Sonos from a 3rd party App. Volume control would be especially nice, but it is a large job to duplicate the Sonos interface. The Sonos controller can be directly called from another App and a simple four finger swipe can return to the calling App.

While not quite as satisfying to the developer's ego as mirroring the Sonos controller, the customer could have full Sonos control following a minimal effort by the 3rd party developer.