For those who don't play F/GO, what does Saint Quartz do? Is it a "restore all units to full health" thing?
It's the stuff you use to roll the gacha, but also can be used to revive your whole team if you wipe on a map.
It's generally not recommended to do that however since you get three Command Seals that do the same thing if you spend them all at once, and they regenerate at a rate of one every day. Most battles in the game aren't that difficult to need to spam revives as long as you strategize and utilize friend supports.
For those who don't play F/GO, what does Saint Quartz do? Is it a "restore all units to full health" thing?
Not only that it also fully fill up the Noble Phantasm of all your characters, as well as reset their skills. Most of the time, your greatest damage usually come from the said character's NP so if you died and used SQ it's a pay to win, although you'll probably get most of yours for free since it's given to players daily like candy.
The reason why people have been using them for revives, however, is due to most newbies or people who started fairly recently having not cleared the story up to a certain point. Right now there is an event that only people who went past a certain point can participate, which rewards a servant who has been long awaited for. However, you do have to go through some of the hardest story maps to get there.
Thus, no time to be waiting for the command seals to regenerate, underleveled servants and likely fairly unexperienced players brute forcing via quartz.
Though I'd have to say, if they are already using quartz there, the event maps itself might be a nightmare for them...