I have a friend who is a pilot for a major U.S. airline, and he collects miles as a backup for pass travel. For instance, we wanted to go ATL-SAN, and the flights were looking pretty full. We had tickets to a concert out there and he was flying a trip until late the night before, so he had a small window of time to try to non-rev on the day of the concert. Rather than risk it, he confirmed a seat using miles a couple of weeks in advance, giving us both peace of mind.