I'm not sure what other practical uses there are for this code, but I use it because I use trigger redirections via PlayerID.
If for whatever reason the PlayerID does not exist, this will allow you to have a "plan B"
type = PlaySnd
trigger1 = PlayerIdExist(var(58)) ;enemy exists
trigger1 = PlayerId(var(58)),StateNo = 1105 ;enemy is in custom hit state
trigger2 = !PlayerIdExist(var(58)) ;fallback code
trigger2 = p2stateno = 1105 ;fallback code
value = 1100,2
persistent = 0
ignorehitpause = 1
For more info on my usage of this see here