Interesting that you should mention this. In the final phase of Nidhogg Ex, there are situational uses for all three LBs. The DPS LB is ideal, but is not necessary to clear. If you're down several party members, there may be a role for a healer LB, unless you're about to get hit with Akh Morn. If you try to healer LB just before Akh Morn, Nidhogg will destroy your stack while your party members revive, and proceed to individually oneshot everyone else. As such, there's also no point in separating someone from the stack as a sacrifice unless the initial target is either a PLD or ideally a DRK (which is theoretically possible, but I suspect that he preferentially targets non-tanks, as I've never seen this happen unless we're down to two members). The solution: Tank LB. Once you survive, your healers can proceed to slowly rez the rest of the party in preparation for the next part of the dance. It's a nuisance, but you can recover from it.

Nidhogg Ex is a fantastic fight to do as a tank (especially on DRK). There are so many ways that you can help your group recover from seemingly fatal mistakes. It almost makes you want to farm it on PF.

T13 is the only fight that I can think of which mandated the use of a Tank LB when the fight was relevant (and it was one of the highlights of the fight). Tank LBs were also very helpful for Ultima HM and T11, but there were workarounds. You could also use Tank LBs to potentially recover from a few potential wipes, such as in Garuda Ex if you killed Spiny too early during phase 3.