Mactabilis

And threat was an issue on most fights in Vanilla, and in TBC. This was back when keeping threat was actually work, and you had people using "Causes high threat"-abilities to DPS. That is why it was relevant. It also stacks a TC effect, making warriors not having to spec into improved TC, that causes points into mitigation. There's a reason why any sensible top guild in the world would give this to the maintank first, then offtanks.

The upsides of having it on the maintank far outweigh the few bosses where thats an issue. I mean, TF was BiS pretty much untill Black Temple for a prot warr, that kinda says it all.

Not really a serious discussion. Its for tanks, I would go MT prio simply because it generates alot of threat.