I haven't reserved two, but I have (and frequently do) reserve the day before I arrive and/or the day after.
We frequently stay at some local campgrounds that are within an hour drive of our home. We get up and leave early, arriving at the campsite well before check in time. Inevitably, the previous occupant is still there and does not leave until the stroke of the hour he has to. So we sit and wait hours until he leaves. We reserve the day before and the site is empty no matter how early we arrive. This is technically in violation of some public campground rules (must be occupied first night), but we have yet to be called on it.
The same for the day after. We will stay late afternoon/after dinner to drive home, well past checkout time. We reserve the day after and do not have to leave early. We tell the CG host we are leaving and he can send any late drop-in arrival to our now empty reserved site.
Since I have the 1/2 price geezer pass the cost for the two extra nights is only one night's fee.