One answer came to me from a friend when I asked why she paid $100 more for a ticket, something domestic, I can't remember where it was to, but it was less than 1000 miles each way.

We live close to MSP, IIRC NW was around $360 and UA was around $460.

She said it was because she had 16,000 miles in her account and this would get her that much closer to 25k for a free domestic ticket.

I explained to her that at that rate (about $100 extra per 2k miles) her "free" coach ticket would cost her $1,250 extra if she kept thinking that way.

I think she felt sick for a week after that, and she is not a dumb person. But, it goes to show that loyalty marketing can work and that the average person does not know what miles are worth on most levels, especially any marginal value the miles may have that you are personally paying for.

I made her sick again when I told her how to get 4k UA miles for signing up for Netflix for a whopping $8.99.