I was outside naxx last night ganking horde and I decided to pop my Cooldowns and go to town on few horde. After I killed them I zoned back in and walked out again to await the return of them while waiting I noticed that my Dancing Rune Weapons cool down was up but my Hysteria wasnt it still had 2min left on it.. So when the horde came back up I poped my Dancing Rune Weapon again killed a horde and zoned in again looked at its cool down and it was off cooldown again
Not sure what else you could use it for maybe if you where attempting a boss in a heroic that is near the enterance and you zoned out before dying :P