As tqFan said, mostly for +1 nightblade, resists and slow res. Item skill modifier on phantasmal blades and devouring swarm happens before global conversion so belt doesnt mess up any conversions.
Global vitality -> pierce on Rancor isnt used for anything either
Well ive been high-rolling a lot of my gear but I never thought about that one 
I think I’ve seen Elemental Bonemonger build that low rolls Vit -> Aether conversions on the pieces.
Adding two more videos before next update. Disengage makes this so much fun to pilot 
Crucible 4:19
Decided to revisit this old build since it has gotten quite a few buffs latest patches. A lot stronger than before and solid all around. Updated OP with new grimtools and up to date videos