After earning a fortune in airline miles, I've figured out the economics of exactly how to spend them

How to spend your miles is a hard question. I’ve gone back and forth on whether to spend as quickly as possible or save them. But I’ve settled that the best strategy is to use my miles strategically so I get the best, most comfortable mile for the buck: I pay out of pocket when I fly domestic, and I use miles to pay for expensive overseas flights in business class, and for upgrades.