There used to be a time when people were kicked from raids if they didn't have their pet on passive . But pets are a lot smarter now though, but still... It makes you a better player if you start controlling it (for one to make sure the pitlord is tanking the doom lords; they need to be attacked by your pitlord). Not even mentioning pet placement is tremendously important in pvp (spell locks, dispels, stuns, correct knockbacks) nuff said, hotkey that shit. I suggest the mousewheel.