We're talking about cross class Fracture for PLD and DRK, who don't have any means to restore TP on their own, and must rely on support jobs for it, or rely on MP-cost GCDs. No one takes it because someone, somewhere did some kind of math or something to somehow prove that cross-class Fracture hurts your PPS. We've never seen this math, though, and I am not entirely sure how it works out that cross-class Fracture (18s DoT vs. WAR's 30s DoT) is a loss. If you're able to manage your TP well enough, I'd think it a very effective tool.