The only downside of this strategy comes from deciding when to make the selection since they don't post instantly, so you need to have them already in your account as a "just in case." This poses a problem only because they expire a year after selection.

Another option, and the one that I intend to use, is to use them in advance when traveling with a companion. My wife and I don't travel together all that often, but we should be make a transcon (not DL's definition) within the next year, so I'll try to book flights on which we can confirm into F at booking.