It's not 1500 - it's 5,000 mile increments. I left off a digit in my earlier example. So if OP had 118k and was buying 3 tickets, they would only be able to use 105,000 of them to discount $1,050 off of the total, or $350 off of each ticket. That would leave them with a balance of 13k miles, which isn't enough to apply 5k more to each ticket.

It might be easier to think of PWM as being $50 coupons that you can buy for 5,000 miles each. You can apply as many coupons to your ticket as you can afford, but you have to put the same number of them on each ticket.

The other weakness of PWM is that you can *only* use them in 5,000 mile/$50 increments. If you want to buy a ticket that is $501, you can either use 50,000 miles and pay $1 on a credit card (along with the TSA fees), or you can use 55,000 miles and effectively pay $550 for a $500 ticket - and STILL have to pay the TSA fees separately.