I think you're conflating very different things. Quotas may be removed if you've got a virtually unlimited amount of a certain resource (and even there they can

I think you're conflating very different things. Quotas may be removed if you've got a virtually unlimited amount of a certain resource (and even there they can be useful to prevent overbilling), but disk quotas are necessary because disk space is not unlimited. Without those, a noisy neighbour can break your application.