Patch 6.1. added a cool new feature that resets cooldowns lasting 3 minutes or more after you kill / wipe on a raid boss.
This can be exploited though.
You can use the cooldown(s), pull the boss and reset the encounter.
The cooldown(s) - i.e. Icy Veins - will continue its duration on you, but the cooldown is reset, so you can use it again whenever.
This basically just extends the buffs you get from your cooldowns by X seconds.
This does NOT work with Heroism, Time Warp or Bloodlust.
Quick note: You can do this more than twice obviously to extend the duration of anything to as much as you want. As long as you can reset the encounter without dying.