It's no longer a desirable offensive cooldown in any situation because of the 7.1.5 buffs, or rather the lack of Neltharian's Fury actually being buffed. I actually think it even got subtly nerfed in 7.1.5 by greying out more abilities that can be used during it / making it harder to accidentally cancel it outside moving.

You'll be using it more when you get 4pc without a doubt, as large melee packs will essentially allow you to spam Ignore Pain without any worry.

Until then, it's strictly an emergency AoE tag / bonus defensive cooldown like it has always intended to be. It is not an "Active Mitigation" ability and should only be use as a buffer to reserve Shield Block charges for when they need used to prevent a mechanic.

Active Mitigation is such a cancerous mechanic. It's bad enough you have to change specs to tank. Doubling-down on "bring the class, not the player" hypocrisy.