Isn't fn.assign useless inside getState?

In my application I call getState so frequently that it even affects performance. I started to investigate and and came across `fn.assign` here:
```js
getState(state) {
if (Array.isArray(state)) {
return state.slice()
} else if (fn.isMutableObject(state)) {
return fn.assign({}, state)
}

return state
}
```

To my mind it's absolutely useless as it does only shallow copy which means inner mutable objects will still be mutable after assigning. Seems that this code just ... slows down performance?