I multibox for the power it brings...to actually have a huge proactive impact in pvp. I'm pretty sure horde outnumber ally on Frostmourne, I'm just helping even them back out :P

Nothing better than 1 shotting someone.

As for what would I trade to go back to single boxing...revert the lifebloom nerf, leave it at 10 second duration, make the mana cost the old value and increase the healing co-effecient for it. And revert the Wild Growth nerf too.