Not seen this posted anywhere yet so here we go!
In phase 2 on the Lich King fight, 1 (in 10) or 3 (in 25) people will be grabbed by valkyrs who will start making a dash for the edge, normally this needs all the DPS to be hacking away, slowing, stunning to free their team mates.
However, if a Warlock stands at the edge with their portals deployed their valkyrs, should they be snatched, can be completely ignored!
As soon as the Valkyr releases the warlock they can port back onto the platform and either help with the other adds or get right back on the Lich King.
Any time a warlock is snatched it will really help you out!