Cryptocurrencies are electronic cash, and as such, will be used by electronic agents to exchange value, verify contracts, and track identity and reputation. All of a sudden, the computing resources spent by the Bitcoin miners doesn’t seem wasted – it seems efficient, given that it can be used for congestion control and routing of other network resources.
Cryptocurrencies are an emergent property of the Internet – almost a fifth protocol in the Internet suite. If Satoshi Nakomoto did not exist, it would still be necessary to invent them. Someday, they will be used by the machines in our network, on our desk, in our garage, and in our pocket to exchange value and achieve consensus at blinding speeds, anonymously, and at minimal cost.