Quote Originally Posted by Crissy View Post
I know when to do it in order to get the boss within the quick-kill margin.

In five of six tome runs through Fractal Continuum, the caster let loose at 20-25%. No disaster, but we wasted time on one more wave of walkin' clocks than we had to.
Disregarding that caster LB is stronger than MCH/BRD, there is no magic quick-kill margin on the last boss of Fractal. Nothing about the boss is HP-based. It's time-based on a rotation. He doesn't take more damage when under a certain percentage of health, so he won't die any faster by holding the LB.

DPSing for 30 seconds, LBing, then DPSing for another 30 seconds is the same amount of time as DPSing for 45 seconds, LBing, then DPSing for 15 seconds.

You will never have to kill an extra wave of adds because someone LBed earlier.

The only argument for holding LB would be if you're not sure if you can kill the boss before adds even with LB, so you'd use the AOE of the LB to kill the adds at the same time as hitting the boss, which the caster one is arguably better suited for as they position the LB separate from themselves, while a BRD/MCH would need to stand on a platform that's already lighting up and carefully line themselves up to hit a maximum number of targets.

However, since you're a MCH, you actually would want the person to use the LB sooner than 20% HP if it's up to LB2 by then because the sooner it hits 20% HP, the sooner you can use Heartbreak, which would be a DPS increase for you, especially if it doesn't die within 30 seconds of hitting 20%.