Necromancy in general just give you a way to sustain yourself through innate life steal from leveling it up, along with blood + drain and Mosquitoes swarm.
Atm, for playing any knife-related character, just go dual knife, vault and backstab people to death. Necromancy will help you sustain while you deal massive damage per turn if your weapon isn't bad. Sadly, atm, Perma CC > Sustain. It doesn't matter if you have 999 health. If your armor/magic armor is depleted, you can perma CC someone with stun and knock.
