My experience is books that are free that are already released you don't need a CC on your account but you do with all pre-orders that are free. I have never been charged anything for a free pre-order. I always remove my CC from my account after I am done ordering due to auto buying by accident once when I meant to send myself a free sample.
So the only time I need to enter my Credit Card information is when I do a free-preorder or buy something from there. If the book is free and already published I just click buy now and it's ordered no CC info needed.
