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.Activate();
         PlayGamesPlatform.Instance.Authenticate((bool success) =>{
             isUserLoggedIn = success;
             LoadHighScore();
         });
         //Social.localUser.Authenticate((bool success) =>
         //{
         //    isUserLoggedIn = success;
         //    LoadHighScore();
         //});
         if (isUserLoggedIn)
         {
             GoogleLogout();
         }
     }
 
     public void GoogleLogout()
     {
         PlayGamesPlatform.Instance.SignOut();
         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?