It's 300 potency over 30 seconds and is not affiliated with any of the WAR buffs/debuffs, not simply "300 potency". It reduces effective uptime of debuffs by 2.5 seconds, and doesn't generate Wrath. If you ignore debuffs and Wrath stack generation, Fracture amounts to just over a 2% increase in damage. When you factor in reduced uptime on buffs/debuffs as well as the reduction in Wrath stack generation, Fracture actually ends up being a noticeable DPS loss (and significant increase in TP consumption, as well).
The only reason for a WAR to use Fracture is for the damage while they are leveling or as a "timer" if they have no other viable method of tracking 30 second intervals (like, you know, a "/echo blahblahblah <wait.30>" macro). At 50, it's a straight up reduction in performance to use it.
