If you like a particular movie or clip and want to watch it multiple times, you can rent or own it. You get so much more when you log in. It's free!
There are two main ways of getting your premium porn on the internet. There is the classic way of paying for a membership and getting all the porn of one site or network, plus all the new uploads that they include in the collection. And then you have the VOD options, which is Video On Demand, basically a pay per view, which only charges you only for the content you want to watch. Because why buy the entire cow for a pint of milk. Maybe you just want some specific movies of your favorite porn star or the kink you enjoy the most.