Originally Posted by redtop43

Let me give an annoyingly technical answer.

Everyone (implicitly, not explicitly) places a marginal value on their time and pleasure. For someone who is retired/unemployed and bored, and doesn't find mile earning unpleasant, they might be willing to spend an hour to earn 100 miles. For someone who is rich and busy and dislikes this stuff, they might need to earn 100,000 miles for it to be worth an hour of their time. Remember also that miles are only worth what you can get for them, adjusted for the time needed to find the award. An extreme case would be the President, who has no need at all for flights anywhere. (Please don't nitipick about "he might after January etc." I'm just giving an example.) I have a friend who is relatively well-off but he doesn't mind traveling coach that much, and although he's single, he has the attitude that a woman who would think it's important to fly premium class would be a money-grubber that he wouldn't be interested in anyway. (Again, don't debate this point, I'm just giving an example of someone with limited use for huge pots of miles.)

It's all where the individual's marginal disutility curve of the unpleasantness of mile-hunting relative to alternative activities, intersects their utility curve of the incremental value of a point. Everything that goes into these utility and disutility curves will locate the intersection for that individual.