Language learning is the classic use case, but I also use it from everything from historical facts to encyclopedia entries on a subject I’m trying to master.

Probably the simplest use case to get started is improving your English vocabulary. (Assuming English is your first language.) I try to add a card for any word I come across that I don’t know the meaning of, and it works very well.

Try to learn a different writing system, alphabet or not. Arabic, Cyrillic, Hangul, whatever. It has finite number of cards and you don't need large context to understand them.

A quick and easy one is learning the NATO phonetic alphabet. You can find premade decks for it.

Leetcode patterns, and common problem types to apply those patterns to.