When to use anonymous expression within setState().

I ran into a problem when I implemented the last code snippet in this lesson for the signOut() function. For reference, these are the two versions of the signOut() function within Context.js

// With anonymous function
signOut = () => {
    this.setState(() => {
      return {
        authenticated: null,
      }
    })
    Cookies.remove('authenticatedUser')
  }
// Without anonymous function, ONLY object with update
signOut = () => {
    this.setState({authenticated: null})
    Cookies.remove('authenticatedUser')
  }

So I believe I am now slightly confused as to when you should pass an anonymous function into the setState() method and when to pass an object into the method. (barring of course, using prevState as we do in prior units)

The completed code provided at the start of the course does not use an anonymous function, but in this lesson we do. WITH the anonymous function, however, I notice that the function breaks. The cookie is not removed, and the app redirect to "/" with the application maintaining the current authenticatedUser AND authenticated: null within the Provider's State.

I realize that an anonymous function must be passed into setState() in components when used in event handlers otherwise the function will execute on render, however, I do not see why including the anonymous function halts the function execution and prevents removing the Cookie in this example.

So when should an anonymous function be used within setState, and when should an object be used. (or is something else in my code causing this to break? it is working without the anonymous function expression AND that is what ships in the completed files)