If you spend less than the amount of the fair use limit, you'll pay for with points you have two choices:
Slide left to Earn bonus points: This will be treated like a normal transaction on your account that will be applied to your upcoming bill but you'll still earn bonus points depending on which membership and Experience you're visiting.
Slide right to Redeem and pay with points: You'll lose the full amount of points even though you paid less than the amount covered by those points. Because of this, most members prefer to Earn instead of Redeem when they spend under the amount we will cover.