React - Redux - Thunks and createSlice - when is an 'extraReducer' needed?

I commented on this topic and I thought I should make a new thread.

As the title says, I’m not sure with React - Redux - Thunks and createSlice - when is an ‘extraReducer’ needed?

Why can you use dispatch() on a function that returns a thunk, and not have it mapped out in a ‘extraReducer’ property. Totally confused