In Chinatown, Jack Nicholson plays JJ Gittes who is a private investigator that gets drawn into a large conspiracy that involves the entire city of Los Angeles and an insane amount of property, money, and so forth. It's a huge, huge deal. Central to this is Noah Cross, who is the big businessman who is going to profit from the conspiracy. JJ Gittes has fallen in love with Noah Cross' daughter, Evelyn Mulray. Now, we discover that thisgirl who JJ Gittes has been chasing, believing to be Evelyn Mulray's now-dead husband's mistress is not a mistress at all, but in fact Evelyn Mulray's sister... and her daughter. In the script, Evelyn explains to JJ Gittes just why she slept with Noah Cross and how he had a breakdown after his wife died, the poor chap. It was cut because all it did was lessen Noah Cross' evil, made him too sympathetic and weakened the entire drama of the story.
In "Sins Past", JMS wrote in the scene that Roman Polanski cut out of Chinatown. The whole arc is just a bad version of Chinatown. Not because Gwen ****ed Norman. Simply because it just wasn't that well written.