I want my phone to ring at level 30. I want to listen to my music with earphones at level 5-10.
If I put my earphones in to listen to music and forget that the volume level is at 30, I basically blow my ears out. If I then listen to my music at level 5, stop listening to music, put my phone in my bag and then receive a call… the ringer level is now at level 5 and I usually cannot hear it ring and miss the call.
Android, iOS, and even Symbian has this feature. It’s a simple one. You shouldn’t have to juggle with volume settings every few minutes with what you consider a smartphone