Dark Intent.
If you put it on an Arcane Mage, the only thing that happens is that two people get 3% haste...and that's it. The casting Warlock doesn't see increased DoT damage, neither does the Mage, and the Boomkin, Spriest, and Fire Mage are all twiddling their thumbs wanting to punch a half baked apple pie just cause it'd feel better than an Arcane Mage with DI.