Pets also feature strongly in the late game. Two of the best items in the game are a scroll of taming (converts nearby monsters to pets) and a magic whistle (summons your pets). Eventually there's no point in fighting yourself; blow your whistle and let your pet dragon army clear the room.
I love the family dragon army! But why bother using taming scrolls when you can polymorph control yourself into a dragon (taking off your armor first!) and then sitting to make eggs where they are actual family! Blood may be thicker than water, but dragon scales even thicker than blood!
Purple worms also make magnificent pets. Genning up a fleet of pet purple worms and teleporting them away can make life a lot easier on the Astral Plane.
Eh, depends on what class you have. Pets are a bit of a hassle to get up and down the stairs. If you do enough damage yourself, it's usually less annoying to do the fighting yourself.
