Darknet marketplaces.

It's responsible for facilitating a ton of fantastic trips amongst myself and friends.

We had extra money. There were some people on the Netherlands with some extra lsd. We swapped using Bitcoin. Value was created.

I genuinely believe this is a valuable use of cryptocurrencies.

That said, I would wager enormous sums of money that on net, they have been dramatically negative. Once you factor in the vast quantities of energy wasted (even using up energy that would have otherwise gone to waste simply decreases the demand for batteries or competitiveness of other marginal-value uses) and all the funding of crime such as theft, fraud, hitmen, blackmail, money laundering, scams, and so on it’s very hard to see “I was able to get LSD” as compelling.

And I love LSD.

As an example it's much easier and cheaper to send money from a bank account in US into a bank account in another country when you use bitcoin as the rails for this. All of this can be done fully legally, using companies like Strike, Revolut, Relai or similar. If you ever tried doing international wire or even using Wise, you will definitely appreciate bitcoin.