I'm thinking to create tutorial pages (visible only if logged in) for my client. Using same CMS database. My question is, is this bad for SEO? should I tell robots to ignore these pages?
Yes it is definitely bad, if your intent is to be searched for the content protected by your cms login system. In this case you don't need to tell robots to ignore the page as the spider will automatically do, they can reach your login page, but not the page that are protected from outside the login system.