In the case of porn sites they're forced to go through third parties which charge very large fees for each transaction.
Pot stores are also cash only. Unfortunately cash isn't possible to send digital which is what cryptocurrencies essentially want to be (the term "digital cash" is sometimes used). Interestingly there have been reports of pot stores going bankrupt when the nearby ATM has been removed.
The difference between 3rd party services like credit cards, PayPal, Apple Pay etc and cryptocurrencies is that nobody can prevent a payment for any reason.
This is also why it's better to donate to Wikileaks with cryptocurrencies instead of PayPal since PayPal can if they want to freeze Wikileaks account. In fact this has happened .
Another difference is that you don't need to trust a 3rd party to deliver your payment. This is why you can't send money to Venezuela via Western Union but you can with cryptocurrencies (as long as they have internet of course).
Leaving Venezuela's border means you'll get searched and forced to leave all your belongings. It's therefore very hard to bring your wealth with you as you'll most probably lose it or you can't carry it. With Bitcoin for example all you need to do is memorize or write down a 12 word seed and you can bring as much money as you want with you.
Finally it's very difficult to make digital payments in today's world if you can't get a bank account. In effect you're locked out of society pretty hard if this would happen to you. Cryptocurrencies are permissionless and is for everyone.