Good question. UA allows you to cancel, and then rebook within a year to any location with only the change fee. On a paid business class ticket, definitely worth it. Austrian, on the other hand, requires rebooking prior to the original trip to the same location and in the same class. That is, in effect, often an incentive to check in and then not show to hope for an IRROPs. They get their money, but probably lose the opportunity to re-sell the seat and collect it twice.