In 2012, the Electronic Frontier Federation (EFF) published an information sheet on "Temporary Copies."  Temporary Copies are made automatically by computer systems and are very necessary.  However, having a temporary copy could be seen as an infringing on copyright.  This three-page document provides background, the EFF stance on the matter, and even an overview of a relevant U.S. court case.  If you find yourself talking about temporary copies, this document might be one you will want to refer to.