For someone who scrapes the cash together for a once yearly trip that's easier than said than done - especially when credits expire after a year or so.
Totally understand that predicament. However, that scenario doesn't seem to apply to most Flyertalkers. Aren't most airline credits non-expiring at this point? I also should have mentioned that points bookings also make for a great plan B option.
However, even if you don't book a plan B option in advance, if you travel often enough you can still come out ahead even if you have to spring for an occasional last minute ticket on another airline.