I think walkthroughs takes moste of the fun out of a game. the whole reason by playing a game is to explore.
only when you have played thrugh a game, you can use walkthroughs to see if you missed something.
or if a game developer has made so many endings to a game and its hard to know if you...
maybe when you start to loose count of how many it is. I would say not more than maybe 7-8 in a harem game. starts to get complicated when the game has a story driven nerative.