Being a server and a client

I saw in other posts that we could not be both but your Networking example (CarRacing) shows otherwise,
but i understand that the server cannot be authorative. If each client handles their logic (car racing not much logic there,if there is no bots...) i can a have a server and play in it at the same time no problem. Somebody please tell me if i'm wrong.

 

You can act a server&client at the same time. This setup can still also be both authorative or non authorative.