Enfeebling potency boosts the accuracy/effects of any skill that has a secondary debuff (Shadowbind, Aero, Blizzara, Pounce, etc). Devs said it a while back, and you can try it out by adding/removing a lot of PIE.

Also, Magic Accuracy is the only stat that matters for Sleep/Repose. Magic Accuracy is your success rate of a spell's primary effect, which is the sleep effect.