The director’s cut of a movie is, at least in terms of expectation from the audience, the true form of a film when compared to its theatrical release. However, that isn’t often the case, since many of the cut scenes were cut for a reason. Movies don’t have an unlimited amount of time to tell their stories, hence why theatrical cuts exist.
But director’s cuts sell, so they are constantly being made, even if they don’t add much value. There are cases where the original, theatrical cut is lost from circulation, leaving audiences with a much longer cut for no real reason. If you’re planning on seeing the following movies, you know what cut to avoid.

Donnie Darko
The theatrical version became a cult classic partly because of its ambiguity, but the director’s cut added heavy exposition and explanatory text that many fans felt weakened the movie’s mysterious atmosphere.

Dumb and Dumber
The unrated version restores several deleted scenes that mainly make Lloyd and Harry seem meaner and less lovable, damaging the goofy charm that made the original comedy work.