First, I think Necromancy should be its own school and that conjuration should focus around summoning elementals and animals, and necromancy focused on raising the dead, and inflicting poisonous damage and diseases on targets.

Anyway, it seems to me that its much more convenient to summon an atronach out of thin air and have then fight for you then to find a good corpse to raise to fight on your behalf. What is the benefit to going with Necromancy over Elementals? Is it just an RP or playstyle choice, or is there a specific advantage to going the necromancy route?