Look, I will give you just one example. Look at the mess with the Ashley Madison. Imagine if their users had an opportunity to pay in Bitcoin by staying anonymous or even semi-anonymous. I am sure many of them would choose this option.
Bitcoin can have many use cases like this one in the adult and porn industry, meeting and dating websites, etc. And I am sure it will have after the Ashley hack.
Why is this just limited to adult sites? Using bitcoin could save many people from having their credit or personal details leaked from many other sites. Whenever you use a website you always have to trust them with your details and there's always going to be weak links somewhere and the possibility of hacks or inside jobs.