I think permits only exist for camping/hiking in areas where demand is super high, like Yosemite. The government has to limit access to such areas, otherwise there'd be real environmental impacts/safety issues. I took our family to Yosemite a while back and we had to get reservations ~5 months in advance and there was a mad scramble to book sites as soon as online booking opened.
I'd say this is more of a California thing but my brother talks about camping reservations filling up quickly in Michigan too. It seems like wherever there's camping near a population center or popular destination like Yosemite, you're going to have a permitting/reservation system in place to control access.