Tienes tú....?

¿Tienes tú los libros de la biblioteca? I'm a bit confused. Why write tienes tú, if tienes already means you have, or in this case, do you have? Why the extra tú? Could the sentence be written "Tienes los libros de la biblioteca?" Is there a grammar lesson on this "doubling up" and why it is used, or indeed, do I HAVE to use it at all? Thanks.

Tienes los libros de la biblioteca means You have your books from the library. It's a statement. If you remember, Tienes means "you have" or "have you." The extra tú indicates to the listener that it's a question. It's there to prevent confusion. Of course, you are right that it's not necessary, but it can be helpful. Just as in English, when you ask a question in Spanish, you will also raise the pitch of your voice, as another indicator that you are asking a question.