By far, my preference would be to wing it. In fact, pre-kids, we never made reservations for our camping trips.
Now, with kids, I feel more of a sense of responsibility of ensuring the family can rely on accommodations being available upon arrival. Plus, it helps mom and dad maintain their sanity not having to search for a campground after many hours on the road. Some high traffic locations (California beaches and others) would be nearly impossible to find a site without planning ahead.
Still, I look forward to winging it again in the future.