Cannon fodder seems to be something that a Necromancer will never run short of.
In the eyes of ordinary people, a Necromancer should be the one who raises an arm, and summons countless undead that transform into a sea of Skeletons, overwhelming all enemies.
But in reality, these cannon fodders need to be accumulated and manufactured. Even the cheapest Skeleton bones commonly seen in various films and TV shows are not conjured out of thin air.
To summon a Skeleton, you need at least a corpse, or at least a full skeleton that can be pieced together. Otherwise, if you summon a Skeleton missing arms and legs, you'd have to assemble a few to make a whole one.