Depends on a lot of issues... do you need specific types of parks? in a popular attraction area? do you need hookups? what kind of full-timing will you do... staying in one place for a long time or moving around weekly or every two weeks to explore the areas?
We full-timed for 16 years and if we had to make reservations for all that time we wouldn't have gone full-timing. We likesto explore all areas of a state, not sit in a RV park. We love national parks, state parks, national forest service campground, boondocking and especially done in the West. Rarely did we make reservations unless we absolutely had to be somewhere at a certain time such as visiting family.