That's what DL sells them for. It would be interesting to know how they value them for accounting purposes. I would suspect it's a number somewhat less than $.0275/mile.
The value to FF's varies depending on how many they have and on what routes they use them, obviously. Where I might feel that the only good use is an Int'l B/E ticket, others might find the ideal use is for a family of four to MCO to offset part of their vacation cost.