When you've been on your bike for 14 hours in the cold rain and you can't find a campground to save your life, you'll wish you did a little more planning.
It's almost a necessity now to book ahead of time if you plan on camping anywhere near a big national park in the US (think Yellowstone or the Grand Canyon). You can't just roll up and expect an empty campground. When I was there in July (no holiday weekend or anything like that), the only spot in the entire park ( including campgrounds, cabins and hotel rooms) that was available was one hotel room at the very north end of the park (a 2.5 hour drive). When we tried to book it, someone else had reserved it in the 2 minutes between finding the spot and trying to book it.
All that being said, I love getting feedback from locals on roads to ride while I'm out touring around. Having a guaranteed spot to stay at night is nice and reassuring though. I'm also not one to drop 60 bucks for a hotel room every night when i'm out for 17 days. Finding campgrounds is a lot more difficult than rolling into a Holiday Inn Express