I believe popular locations are the key point, here.
We are headed for the Black Hills in June with a few stops / overnights along the way. I waited to decide on where we would stay there in the Hills for our 4 days planned there in the immediate area 'till early-March, when I had time to look up recommendations and discuss/show it to DW. I figured no big deal being 14 /15 weeks out. Our first choice was already booked solid with only single / 2 day spots available. They where, however, nice enough to recommend a similar style CG a few miles up the road who had a great spot available.
The rest of this 12 / 13 day trip will be no-reservations -- first time for us, and I'll admit my cautious mature has me slightly anxious about it, but I have read / heard enough stories here and from friends doing the same thing, that I'm okay with it.