They give you "Ascended Fury" or whatever now when you start the game. It is there for you to use to fight against these invasions. It basically turns your character into a one man wrecking-crew when it comes to invasions and rifts. Even in a terrible build, you should be able to take down all of the invasions. I actually find it working on event bosses to take away from my fun. Seeing the Ember Island bosses blow up in 40 seconds because a few people pop their Ascended Fury is a bit disheartening and takes away from the "epic" feel of the bosses.
Seriously though, put that ability on a hot bar. I have it on a hot bar in all of my role setups.