The cold hard facts are that Fracture does more damage and costs more TP. Between a randomly given fight its more efficient (even if its only slight) to use fracture. Dead boss 2-3 seconds faster > dead boss 2-3 seconds later. A boss with jump mechanics (disappearing for an attack) its even better to fracture because you have TP cool time. And to those that repeatedly want to bring up "Oh noes... my TP ran out" here's a tip.. if your TP gets low exclude fracture until you can regen more. Until then, bleed 'em up.

^This is all assuming you aren't having enmity problems.