I had just learned Foe Requiem and was at Whitebrim where that fate with all the tons of Ice Sprites popped. I'm thinking "Oh cool I now have a job skill that isn't just relevant when in a party since it's a big AOE debuff that will cause all these sprites to take even more damage from the casters in this fate, even if they aren't in a party with me."

If you can't guess what happened, I'd suggest trying it as soon as you have Bard & Foe Requiem unlocked just to see what a magical experience it is.