What is the use of the `prepare` argument in the createSlice function of Redix Toolkit?

I'm following the Redux tutorial from redux site, and in Part 8, when writing a reducer to handle todos they do the following:

const todosSlice = createSlice({
  name: 'todos',
  initialState,
  reducers: {
    //...
    todoColorSelected: {
      reducer(state, action) {
        const { color, todoId } = action.payload
        state.entities[todoId].color = color
      },
      prepare(todoId, color) {
        return {
          payload: { todoId, color }
        }
      }
    },
    //...
  }
})

They make use of the prepare function; however, I wrote that code without knowing the existence of the prepare function as follows (only using the reducer) and it works as well.

const todosSlice = createSlice({
  name: 'todos',
  initialState,
  reducers: {
    //...
    todoColorSelected: {
      const { color, todoId } = action.payload
      state.entities[todoId].color = color
    },
    //...
  }
})

So why do we need in this case the prepare function? or is it just a simple example where it makes no difference?