It's not really about ordinary users like you. Google is shifting their strategy for Google Drive more towards enterprise, and this is a useful feature for enterprise users. Have you ever seen one of those email signatures stating "this email is property of XXX corporation, etc. etc." or seen an email sent to a large group of people in a company with strong exhortations not to send it anywhere else? This is a strict improvement over that. Yes, people can actively work around the printing restriction, so it's not 100% secure. But people were already using email for sensitive information, and this decreases the ways the information can get leaked from negligence or active subversion to just subversion.