Yes, we usually reserve. Everybody RVs differently, and some of us can't help ourselves. (Meaning - we're compulsive planners.)
I don't want to miss anything or leave things to chance, and really enjoy all the research. I put together a binder of phone reservations or emailed confirmations, street address, and notes on local attractions. If it is a "walk-in, no res" campground, we plan to get there early enough in the day to get a site, and have a plan B in mind.
We pack a lot of activity into our two-month trips and often book raft rides, tours, railroad rides, etc as well. I like to be in a campground with character related to the area (not just a place to sleep), in the best type of site at a reasonable price when possible, and the closest location for our plans.
And in the winter, like others, if we want to get out of the cold for a few weeks and have great waterfront spots in FL, planning ahead makes it happen.
For me, it's very relaxing to wake up, enter the address into the GPS and know how far we'll be driving that day, arrive by mid-afternoon, and settle in to a nice location overnight, for a few days or longer. It's kind of like a caravan. Everything is planned ahead. We've stayed in some great places.
Our trips are busy but not marathons. I build in plenty of time for just relaxing, finding unexpected things, and rolling with the punches of weather delays, repairs, government shutdowns, etc.
When we are heading back to the barn, which can take a few days up to a week, then we take the "see how far we get" approach and just make a phone call to book an overnight each day.
We saw the "campground full" sign quite often in late August into mid-October this year, and not just on weekends. I think that's becoming more common as baby boomers hit the highways.