I agree with physicphairy, even though many users will see this "demo" option as a cheat option that will diminish the game, its a nice idea for those who choose to use it. There have been so many games I have played for weeks, got stuck on a single level and not played the game again for years due to bordem and frustration. What about those times you lose your game saves by accident and want to make a quick journey back to the stage you reached in the game?* I say this is a good idea, cheaters can use it to cheat, genuine players have the option to bypass a stage that ruins their gameplay experience.
*Obviously, some games that are more involved with choices and "collectable" itmes may not be this straight forward, but hey, its better than having to go all the way back to the begging after losing your gamesaves!