For world PvP a four warlock/priest team is quite strong. For PvE, the team gives you the ability to efficiently quest in the open world if you want a break from the dungeon grind of your warrior team. Although it is nice to have the voidwalker pets tank each dungeon once or twice to complete the quests. For PvP, many warlock abilities can be cast without facing your target. So even if someone is running circles around you, your corruption and curse of agony can fire off and the enemy has eight dots on them in an instant.

My lock/priest team is only 28 at the moment as I am focusing on my other team, but the farming potential at max level is huge both in dungeons with VW tank and in OW with the ability to multidot everything.