Originally Posted by
florin
Now think of airlines and FF partnerships. If 2 airlines are partners, it makes sense for them to share award inventory. I.e. all award seats are available to members of both FF programs. Why would they bother paying each other? It sounds like a complicated, unnecessary exchange. Those seats would be empty anyway. Why keep swapping around small amounts of money, when it will likely pretty much even out in the end?
It's easy to imagine situations where there wouldn't be balance in the end. For example, one airline might operate more routes to leisure destinations (which might see more redemptions than boring business routes). Or, one airline might make it much more difficult and expensive to earn or redeem miles. When you have an alliance of several airlines, these differences could be magnified. As another poster mentioned, if there were no cost to airline 1 for booking its frequent fliers on airline 2, wouldn't most carriers prefer to do this? Instead, many carriers make it easier (and sometimes cheaper) to book awards on the home airline.