It partly depends on what sights you are wanting to see. In some places, there are CG's right in town so you can use public transit to get around.
If you stay in some of the National Parks, they have free shuttle systems that get you around even easier than if you had your own vehicle. Zion, Bryce, Glacier, and the Grand Canyon come to mind. I'm sure others will chime in. The downside is that NPS campsites with FHU are either few in number or non-exitant in most parks. Although at Bryce and Zion, the free shuttle system also services nearby areas with private CG's w/FHU.