I like to put my headphones in while I play the game and listen to music. Since the system-wide silent mode doesn't work for this game while my headphones are in, if I want to disable music, I have to go to the in-game settings and manually turn the music slider off.
Games like Bloons Monkey City automatically stop the in-game music from playing on mobile when there's another active audio source like Apple Music or Spotify, and fade it back in when your audio source stops; this behavior would be nice in Idle Slayer too