Airline customers like miles. Research shows that for certain business travelers, earning them may be the most important decision factor of all.2 At any rate, many business travelers see collecting miles as a perk of the job. Stories abound of them going out of their way to fly with this or that carrier to earn enough miles to reach its next status tier or to redeem their miles for a dream vacation. The ability to save up miles for such trips is the reason many customers enroll in customer-loyalty programs in the first place. Eighty percent of all miles are redeemed for flights. (In many programs, they can also be redeemed for hotel stays, car rentals, and consumer products.) In a classic program, 20 round-trip economy-class flights from Europe to North America, at a total cost of around $20,000, can earn a passenger enough miles to redeem a first-class ticket that costs $10,000 - a payback of 50 percent! Get the full story at McKinsey