I prefer a reservation when I have a destination in mind. I may leave the daily agenda open, but I am sure I will have a place to stay.
However...a couple years ago DW said: "No planning. Lets just go for 1o days". What a blast! Drove east for the day, found a place for the night. Wife saw an ad for some caverns see wanted to see, went 1/2 day north...stayed 3 nights. Left there went further north and west, stayed a few more nights. stopped 1/2 way home for another night. Ended up spending 9 nights at 4 different campgrounds. Never left the state of Pennsylvania.