For Prot at least, it's a big part of their survival in PvP. Damage is pretty crazy out there right now - it's not too hard to die within a silence or single root - so I'll take anything to help me out there.
The tradeoff is not being able to use ShotR consistently, but that's the point. Blizz said they don't want tanks in PvP to be gods of damage but really good at survival/utility.
It's not just Prot PvP. I use it all the time in PvE. Once I get a good threat lead I switch to using WoG and use that almost exclusively for the rest of the fight unless I need to get more threat.