I flew last weekend to SLC on SWA and booked business fare, just to try it out. It was good to check in 2 hours before the flight and get position A3, but really not a big deal. However, on the way home, I experienced the real advantage. My fight was delayed several hours, so I switched to another flight at the last minute. Even though the flight was full and almost everyone had already checked in, I got position A7. Money well spent.
