Just curious about "Passport America"

There are a lot of variables. We've belonged twice. In both cases, we found a park where we wanted to stay for a while which happened to participate in Passport America. We purchased the membership from the campground when we arrived, and got the discount - and they were very accommodating because we were buying from them (I think they get to keep most if not all of your membership fee if you buy from the campground).

After our initial buys, we did use the discount a few times, but we didn't use it often because we based our location and campground choices on other factors. When each of our memberships expired, we did not renew, because we had learned that we could join on the spot if we happened to choose to stay at another Passport America campground.