Some people--me included--believe that centralized systems for basic things are bad because of their single points of failure, whether physical or merely administrative. If you believe that centralized databases have value, and you believe that decentralization has value, then decentralized databases sound useful.

Honestly, most centralized databases are used for silly things you would disagree with also, and the ones that aren't are often used for financial services that you are going to claim are somehow not ok when decentralized but totally fine when centralized :/.

FWIW, I've been using it as a fully distributed replacement for the Tor directory servers (which are run by 9 people as a form of charity, with no plan when I have talked to them for how to deal with people coming by with crowbars to threaten them) and then people pay for their bandwidth (allowing for both fair allocation of resources and well as incentivization of supply), which of course fundamentally requires a programmable decentralized currency (which is itself just a program running on the programmable decentralized database).