To those of us who are lucky/rich/spoiled to have an Ethreal Soul-Trader from the WoW card game know that these guys take souls from the guys you kill, and you probably know that they take their sweet time with it.
Turns out, that when you do the Argent Citadel dailies and you have this pet out, if you kill the foot soldiers (by running them over) ,the ethereal will take almost ALL of their souls at the speed at which you kill them at.
This would probably be useful for farming the mutagens or the pieces of armor he sells. (Because nobody wants to kill 2000+ mobs non stop for an ethereal suit)
Hoped this helped somebody.