You can book 2 nights and only stay one night. In some cases having 2 nights can be useful. I don't like wasting points, but sometimes it's so worth it.
Scenario 1
I have January 17 and 18, Saturday and Sunday night, booked. We won't be arriving until the 18th but have a very early morning flight and will be at the resort by 9-10am. Instead of having to potentially wait who knows how long for our unit to be ready, our unit should be ready and waiting for us when we arrive
Scenario 2
Again using January 17 and 18. We have an evening flight on the 18th or the resort is only a couple hours drive from where we live. We don't want to have to be up and checked out of our unit by 10am. We can sleep in, have a relaxing brunch, use the pool, or whatever to enjoy the day before we have to leave for the airport or the drive home.
Scenario 3
This one probably applies to us more than most people. Back when we only had to book one night that meant we were up and on the road again the next morning after a long day on the road the day before. If we've had an 8-13 hour day on the road, getting back on the road to do it again the next day is something we have done and could do; we just don't want to now. Thanks to the 2 night minimum, we discovered how much we really like not having to get back in the car the next day.