I think it could be used for some kind of permissioned, collectively crowdsourced database that's (mostly) free from the control of a single group of administrators/gatekeepers. I guess kind of like a decentralized wiki.

In my view, blockchains shine where you need auditable global state, bonus points if you don't want central control in your operations (obviously this then kicks the can to the core devs). This use-case is fairly miniscule for most applications, though.

As far as currency, I think they also have their use-cases as well but most people don't want a global audit trail of all their purchases. Things like Monero and Zcash shine here. The value fluctuations are obnoxious, though.

I'm saying this as a big blockchain skeptic. I think most of the things people use them for are silly.