Any “boarding upgrade” on Southwest is contingent on you being present early in the boarding process and scrambling for a good seat. If you get to the gate just before departure, your “upgrade” is worthless.
On other airlines you have an assigned seat, so you can just sit in the airport and board last if you want and you still have your seat. This matters if you are running late one day. It also means you have to allow extra time when flying Southwest, as you can’t use the boarding time as buffer time, at least not if you care what seat you’re in.
