If you have no NIN in your party, helping out the first tank in building extra enmity is better for everyone. Diverting 25% of your current enmity means that when you provoke off the MT, your own enmity will be 25% higher too. If the other tank then shirks during the swap, both tanks' enmity lead on the boss increases, and so on. It's useful for raids and trials only.

Or if you want to troll Duty Finder dungeons, I guess.