Because I like the idea of making a witch. With alchemy and enchanting no doubt.
So yeah, no doubt that I will use a blade as some sort of ritual weapon. (Miraak's sword, I'm coming for ya!) Light armor aswell, because Vampire armor.
And destruction magic, though I'm not sure between shock and frost. Frost is awesome looking and fits a Nord in the first place. But shock seems more traditional for a witch.
Anyway, back to the question, Necromancy.
I want to use conjuration aswell, but I don't really like the idea of atronachs for this one. So Necromancy is probably better.
But Necromancy? Would that be one of the things that you could consider "witchcraft"?