Nextcloud asked in a poll at https://mastodon.social/@nextcloud@mastodon.xyz/115095096413238457 what database its users are running. Interestingly one fifth replied they don’t know. Should people know better where their data is stored, or is it a good thing everything is running so smoothly people don’t need to know what their software stack is built upon?
For most applications the overhead of running a second DB server is negligible.
And if it’s SQLite (which I believe is the default) it’s really just reading and writing a file on the file system.