There is another way for over-provisioning as well.... just don't fill the drive up!
IMO, this is the best way since it allows the greatest flexibility. Sometimes, you may temporarily need that extra space. You can set a quota in the OS to warn you if you exceed a subjective limit. An enforced over-provisioning is really only needed if you have some unmanaged servers.
However, you are correct. If you create a 60GB parition on a 80GB array, that would be a 20GB over-provisioning (which is excessive for common desktop usage).