The best movies are made in the editing room. Of the reels and reels of film shot for any movie, a large part is cut to bring the story down to two hours or so. What's not used can be released later as a bonus on home video media, or as a viral boost when viewership starts to flag. But sometimes a scene, a character, or a whole subplot is cut because it was just a bad idea all around. Some of the best movies have such scenes, and it is only a long time later that we learn about them. But when we do, we understand why. Some of them will make you say, "What were they thinking?"
Imagine nudity in The Breakfast Club. Imagine an on-screen murder in Back to the Future III. A sex scene with a ghost in Ghostbusters. Yes, it was a good idea that those were rethought and cut from the movies. How about a sex doll in The Thing? Or cute little Elliot getting a lecture on drunkenness in E.T.: The Extraterrestrial? Those are things that might have been, and would have hurt the movies overall. Read about those scenes, with video evidence for some at Cracked.