Is using a spotter on squats actually a thing?
Yes.
What possible help is he providing?
Since your core usually gives out before your legs, he or she will provide just enough force to keep your torso up past your sticking point.
You're either going to lift the bar up and set it back or you're going to throw it on the ground and Roast Beef shame style take the weights off the bar from the floor.
With a spotter, it always gets up and reracked and that way you don't have to dump the bar (potentially bending it as it hits the rails), and if you don't dump the bar that means you don't have to unload it, rack it, and reload it.
One time I was trying to impress a brother and the bar just rolled off my shoulders and landed squarely on his foot while I attempted to walk away like a girl with a groin injury. Then I yelled at him for being so close to me. Because clearly, he was the reason I couldn't complete the lift.
If you're doing a low bar squat, it's more useful to have a spotter since a tired torso tends to fail forward.