I've used them a couple times as part of a group camping sites in Michigan, but after seeing them in Iceland, I have become a HUGE fan of just having a grassy area for tents. Pay a smaller fee, pitch wherever you wish in the area, maybe have a couple community picnic tables and campfire pits scattered around the area. Always have room for one more camper, and you can leave the designated spots to the ubiquitous RVs. There really is no downside, nearly every campground I've been to has an area that could be utilized for this quite easily.

Even when car camping, I have no need for a $35 a night site with full hoookups, just a place to pitch a tent and some sort of toilet facilities.