A warrior's enmity combo, Butcher's Block, is their highest potency combo. In comparison, a Paladin's Rage of Halone combo is 90! potency less than Royal Authority. So naturally a Paladin will want to avoid using RoH as much as possible, while Butcher's Block is a natural part of a warrior's highest DPS rotation. We've already established that PLD/DRK benefit from holding the boss's aggro, but almost ironically they are the worst classes to generate hate with. Warrior is the only class that can almost completely negate the damage penalty of their tank stance thanks to Unchained, and it would be a waste to not let them do it. One fell cleave does not make up for both tanks getting to stay in dps for the entirety of a fight. Pacification is a convenient time to provoke, and remember you can accomplish all of this without the need for shadewalker from a NIN.

Of course we're talking about high level play, not your average pug.