I do that mostly to meet FC demands. Blessing and a curse from how I see it, because as much as I'd like to have every job geared for every circumstance, at least trying for it means that I can provide more opportunities for friends and FC.

It helps to prioritize though. Like for Stormblood, I plan on no more than one 70 per extended role (one tank, one healer, one ranged, one melee). No idea if I'll stick to that, but at least that way I won't get too obsessed with gearing up every single job.