I don't know where this idea has started or why it's so spread, but for the past few patches, I've noticed an increasing amount of tanks and cotanks using Provoke/Ultimatum as a regular part of their rotation and its become such a pet peeve of mine but there's no non-rude way to point out how ineffective it is. I don't know who's spreading this misinformation but I feel like it has to be from somewhere with how much I'm seeing this lately and it needs to stop.
For those of you not in the know, Provoke and Ultimatum work by matching your aggro to top aggro and adding +1. So if you're already top, you're literally only adding the lowest tick of aggro you can to your current and now they're on cooldown so if something happens to you or a cotank, you won't have them up to take the aggro off of your party members!
Save Ultimatum and Provoke for when you need to pick something up such as when you died and were raised or the main tank dies or a tank swap is necessary.