The issue is that when you kill a channel to play an SFX the music sounds like absolute garbage. There are lots of examples of this.
For doing this right, the music should be made for 3 channels and leave 1 free for SFX, but I guess most people didn't want to do the things they had to do on the inferior machines like the 64 or MSX anymore, so they went full on and used all tracks for music
I believe phx made a pretty clever system for music+sfx when he ported sqrxz.