If you're WAR and you have someone sleeping other mobs -> Flash. If you're PLD, CoS -> Flash until half regardless of if there's someone sleeping mobs. If there's someone sleeping mobs, though, don't CoS again when it's off cooldown and make sure you flash after every combo on the focused target. Only useful for WAR on multiple mobs, but also useful for PLD on single target enemies due to the Blind effect from the trait.