Gives your fatty evasion and gives you blockers. Best used on a hexproof creatures; the best being Plated Slagwurm, Thrun, and Troll Ascetic, all of which are hard to kill (toughness, regen), the hexproof helps with most aura issues, and all of which lack evasion.

Things like that make it so you'll reliably get your saps and helps your damage get to the "red zone." You'd usually want something else, but it does work well enough with them.