If you know for certain that you are going to be in an area I think it is a good idea to reserve. If you are unsure of where you will be, I don't like to commit myself anywhere. For example, late May I am taking off for 16 nights. I am heading straight down to Hells Canyon National Park area in Oregon, so left the first night open to stay wherever, but booked the next 5 nights in an Wallowa Lake State Park just outside of Hells Canyon. The next 3 nights at Ranch (in my trailer) in NE Oregon where I meet a bunch of photography friends. After that we head to the coast and the next nights stay will be wherever as well as we will be travelling. I then booked the next 2 nights at Umpqua Lighthouse State Park just north of Coos Bay where the rest of my friends are getting a room. (Can you tell I like the Oregon State Parks
) After that we have 4 more nights to meander our way back home and will likely just wing it for places to stay as we don't have a set itinerary for that period of time.
So to directly answer your question Glenn, if you know for certain that you all will be staying in that area, I would book for sure. You can usually cancel with only a small booking fee if you need too.