What's the difference between PlayGamesPlatform & Social.localUser?

This is my code for Google Play Services Login, which is called by a button press in another class.

public void GoogleLogin()
        PlayGamesPlatform.Instance.Authenticate((bool success) =>{
            isUserLoggedIn = success;
        //Social.localUser.Authenticate((bool success) =>
        //    isUserLoggedIn = success;
        //    LoadHighScore();
        if (isUserLoggedIn)

    public void GoogleLogout()
        isUserLoggedIn = false;

You can see that I commented out Social.localUser.Authenticate and replaced it with PlayGamesPlatform.Instance.Authenticate.

It works the same both ways, so what’s the difference?

To me the only difference (that forces to use PlayGamesPlatform instead of Social.localUser) is that there is no way to manually sign out the user with Social.localUser (this is a required feature when developing for Android).
So if you plan to release your app on iOS and Android, you have to use Social.localUser for iOS and PlayGamesPlatform for Android.