I never whistle as I drop it (pet hate) but I do always signal that we are ready to restart, after play stopped for a serious injury, by blowing the whistle.
Especially useful where, in most cases, players have left positions to get a drink or see if their seriously injured team mate is ok. A whistle is a useful, right we are ready to restart now, wait a moment until everyone looks ready and drop ball.
I'm not sure why they put dropped ball in that last list. It doesn't make any sense. What if a substitution happens before a dropped ball. I doubt it means that if it's a dropped ball it negates the need to blow the whistle after a substitute. Or if a player is sent off for VC against an outside agent. Logic, to me at least, says it is the other way and that you have to when it's one of the 3 (YC or So, sub, injury) and not for any other dropped ball type.
Same with a GK. No whistle needed. But if a GK comes after a substitution you do.