Other than glamor usages and putting an arbitrary restriction on who you're allowed to enter Frontlines with? They're never relevant in the story (Aside from like 2-3 lines of dialogue when talking with some NPCs where they just mention your rank), they have no storylines of their own, the gear they give themselves is only semi-relevant when you're first leveling up. I mean sure you can buy items with GC Seals but is that really all they're good for? Being yet another currency vendor that could just as easily be assimilated or replaced with any of the other ones?

So what are they for? Because right now they just feel like some half-baked idea they implemented only to put no actual content behind it.