Purpose: Completing the quest chain turns your spell graphics GREEN!
Source: It drops off the rare mobs on the Isle of Thunder and is only lootable by a warlock. Even if someone else has already tagged the mob you can still assist without being in their group or faction. (If you can't loot a mob log out and back in). Many warlocks are posting saying it took them up to 100 kills.
Bragging Rights: Getting it seems to be the easy part though as the final fight is rough to say the least. 490 ilvl is the minimum it has been completed with, closer to 500 would be beneficial. Having the gear of a raider won't be enough though, this fight is very complex and requires alot of awareness and execution.
Here is a link to a full guide written by a warlock: http://eu.battle.net/wow/en/forum/topic/6877337992?page=1#0
P.S. Has anyone on our server completed this quest yet?