I never changed to the Slayer(on purpose, that is) and had no problem finishing the game.
From what I read, most people use it to lower their reputation when necessary to keep non goody goody NPC types happy when rep gets too high.
A high level fighter-type is probably better off with his equipment, but maybe a protagonist thief or mage caught in a bad situation could use it?
------------------
An elevator smells different to a dwarf.
