No, it wasn't mileage runs that I was thinking of, although both of you have identified cost/benefit arguments there. Many of the items on the list have arguable cost/benefit balances, both ways.

But there's one item of behaviour on TomBascom's list which tends to depress the revenue earned by the airline from the passenger, while clearly adding to the airline's operational costs in relation to that passenger as well as the contingent frequent flyer liability costs.

The fact that it doesn't stand out like a sore thumb here demonstrates, if I may say so, my point that this forum is not really a good place to debate this issue. Collectively, our focus is on what we can get out of frequent flyer schemes and we're very good at it. But collectively, we have relatively little real understanding of how airlines work as businesses and of how the schemes relate to the operational business - particularly in numerical and financial terms.