I found out about these just yesterday, and I think the main use for them would be for using Redux within a custom hook. This means you can have shared Redux functionality without the need for exhaustive use of connect().
However, now that useReducer() is built-in to React, I'd be interested to see if it turns out to be a decent replacement for Redux. Especially in cases where shared state is needed in a large section of an app, but not entirely globally.
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