FoF with 2pc is roughly a 3.4% dps increase over not using it at all. Lets say you're doing gara'jal and you're staying on the boss instead of going under, 6 minute enrage timer. 6 * 60 = 360 seconds, assume that you play your monk very well and put a staple dps of 63k, 63k / 1.034 = 60928.4 dps. 60928.4 * 360 sec = 21934235.98 damage. 63000 * 360 = 22680000. Not using FoF would be 745764.02 damage in total lost during the fight..or roughly .6% of the bosses health pool. Now, its not often that .6% hp makes a large difference in killing a boss, but it CAN. Even on heavy movement fights, during the periods where you won't be moving it will still be a gain to use FoF.