well, actually it is. it renders your phone useless (can't browse web, can't make calls, can't text, etc, etc otherwise you lose the chromecast monitoring. if it was native, you can cast the camera and use your phone like normal.
Good point I only use the phone to cast, and have another phone to use as an actual phone so never really thought of that. Your battery won;t last very long casting though, better make sure you sit near a socket