I consistently book weekends we think we "might want" months in advance. We also pay for the entire stay in advance, and we certainly don't have a $250K rig.
With Indiana state parks, the reservation window opens up six months ahead of time. There is a run on the best sites, with people sitting on their computer to book them, so I have no choice but to play the game, book the sites, and then cancel if I can't use the site six months from now.
If I wait until the Friday of that October weekend, I won't get a site. That park, and all of its 600 sites, will be sold out. I have to book that October weekend in April. If I can't go, I cancel as soon as I know I can't go.