Are researations needed most of there time anymore?

We did 13 states between Aug.15th and Oct. 3rd. May have made one reservation the rest was wing it and we were not turned away. One campground was a first come first served. Stayed two weeks at one place.
stayed at a few KOA's and they still had sites when we got there without reservations. This is how we usually travel. Has worked for us for the last 17 years.