We rarely make reservations in advance.
This past summer, we were on the road for 10 weeks and made only one reservation before we left home. That was for Yellowstone National Park. Ordinarily, we would not have made that reservation, but this time we were meeting Sarah's brother and family. Since they were on a fixed schedule, we made reservations early in 2015.
We made a second reservation in mid June for the fourth of July.
While traveling, we decide where we want to get to around 3 PM and call to see if a spot is available. Rarely we have had to choose a second spot.
Tom