As a warrior, I use this trinket on Kidney Shots, most forms of roots (Frost Nova, Entangling Roots if Pummel is on cooldown etc.), any stun effect that interrupts my adavantage in a fight and all pally stuns.
Those are dumb reasons to use the trinket. A good rogue will ks u, once you trinket you are now blinded for 10 seconds while the rogue switches targets and smashes your healer. What? The blind is almost over? Unfortunately since you did no action for 7 seconds, you are out of combat, the rogue has walked over to you and performed a vanish sap. Congrats, you've been out of the fight for 20 seconds.