Another great reason not to. I am a WAR, a MNK, and a WHM, and let me tell you, if you are going to DPS, you should just stick to Aero for DoT and Stone II for attack. A tank is going to usually direct and command the dps based on their tank style. They are responsible for controlling the mobs so why shouldn't they be allowed to have full say in how they tank? They will want to minimize any possibility of losing control. You are clearly working against that. As Summoner stated, a MNK will lose its greased lightning stack therefore losing alot of DPS until they can go through the combos and get the stacks up again. To get 3 stacks, the monk must do 3 combos. So not only did you take some degree of control from the tank, you took valuable DPS away as well. As a WHM i use it as a last resort, but you are just being irresponsible, and completely inconsiderate to the rest of the party. If anyone was the problem it was you.
