At the risk of drawing ire and vitriol from others, I will confess I have done something similar.
There is a popular NF CG less than an hour drive from our home. In the past we have made a reservation for a block of days. We arrive well before noon, as it is a short drive, only to find it still occupied from the previous night's user. So we have to sit and wait for the occupant to pack and leave, which is usually at the stroke of the checkout time or a little past. Same on the last day. We wanted to wait after dinner before packing up and leaving, but the subsequent reservation holder had already arrived and was waiting for us to leave.
To solve the problem we began making the reservation for the night before and after our intended stay. Then our reserved site is empty when we arrive and we can stay late on our last day. Since we have the pass the two extra nights are half price apiece, so the two extra nights are the price equivalent of only one night.
I do feel bad reserving the two extra nights we do not use, however it solves the problem of our early arrival and late departure.