Use React for ephemeral state that doesn't matter to the app globally and doesn't mutate in complex ways. For example, a toggle in some UI element, a form input state. Use Redux for state that matters globally or is mutated in complex ways. For example, cached users, or a post draft. Sometimes you'll want to move from Redux state to React state (when storing something in Redux gets awkward) or the other way around (when more components need to have access to some state that used to be local).