The Lemmy app we are using on our phones needs to download content from Lemmy so it can be displayed to us. Lemmy might just have one big file full of links, but that’s annoying to have to write code to handle. Or it might have a folder full of files where each file is a post, but that’s also a bit annoying to write code to manage.
It (probably) uses a local SQLite database to store all of the cached posts.
Conceptually, a database is just a place to store things, just like a big text file. The database just handles a lot of the grunt work for you and makes it easier to search, organize, and filter the data.
So anywhere there is data, there could be a database.
If you’re memorizing your password, don’t change it too often because it’ll just confuse you and encourage you to pick easy to remember passwords which are less secure. Change your password if you hear about a hack, or have reason to suspect your password got leaked. Otherwise there’s no need.
If you have a password manager though, go off. Change it as often as you’d like.
(Also 2FA, unique passwords per site, etc etc etc)