How important is it to have rules for magic that prevent magic-users from being too powerful? I have noticed that if a magic user is not somehow limited in his magic using ability then a group of people in a fantasy story wouldn't need to travel by horse, because they could simply transport wherever they wanted to go. The party get captured - no problem, surely a magic user could just turn the prison walls to mud. It gets silly because a magic user could potentially do anything. Hence you need to limit magic in scope (how many spells a magic user can cast), potency (how powerful a spell the magic user can wield) and frequency (how many spells a magic user can cast at any one time - otherwise even a single, low powered fire spell could be used over and over again to almost invincible effect) But how important is this need to limit magic and let the reader know that magic users' power is limited? Do fantasy readers even ask these questions when they are reading fantasy? Also another question - how can a writer succesfully merge fantasy and science fiction - and bring magic into a technological, futuristic setting? Any thoughts?