the Jester
Legend
Sleep is an automatic hit affecting 5d8 hit points of creatures. +2d8 for every spell slot above 1st. Can you see how this in a monster caster's hands might destroy a party without getting to make a saving throw?
Except in 4e where you need to hit, sleep has always had the potential to wipe a low-level party. I've still never seen it actually happen, though.