In my limited experience, the only usefulness is to trivialize content by allowing you to circumvent intended mechanics.

For example, the tank LB means you can ignore the pillars in Garuda, story mode. It's obvious the designers wanted players to watch their positioning and not splash the pillars with AoE, and it's fairly obvious that they wanted us to AoE the adds down before they did significant damage to the pillars, but you can pretty much stand anywhere and casually kill the adds, using the tank LB for her ultimate.