There's a pattern I see constantly: every piece of UI state gets its own useState, the component re-renders on every interaction, someone adds useMemo to fix the performance, and the whole thing gets progressively harder to follow.
Most of that useState wasn't necessary.
useState is for values React needs to track in order to render correctly. Not every value in a component qualifies.
Three things that routinely end up in state when they shouldn't:
Derived values. If you have items in state and you're also storing filteredItems in state, you have two sources of truth that can diverge. filteredItems isn't state, it's a computation.
