Heard an excellent quote
...on the most recent episode of "Risky Business": "Cryptocurrencies are basically an Internet-wide bug bounty." (I don't have the audio at the moment; the wording may not be exact.)
It does seem to be the most consistent use for them: as something for criminals to steal, or extort, or to get other people to unknowingly mine. I think I'll start my own crypto coin and name it the McGuffin.