They're a sort of cross between an Achievement system and an in-game gatekeeping system. Want to see more humiliation content? Unlock the "Commoner" Quirk on Luna and more humiliation stuff with unlock too! Don't like it? Just don't unlock the Quirk :)
That being said, most of the Quirks don't unlock extra stuff right now - that'll be added later, once more of the important stuff is out of the way.