A lengthy post here notes that Episode I (the fourth movie made) of the Star Wars saga is almost entirely superfluous to the story arc of the other five movies.
While the fact that this is the case is more or less irrelevant, since Star Wars fans will watch them all sooner or later anyway and probably already have done so.
I point the post out mostly because while Episode I wasn't canned by George Lucas who had immense financial backing due to the success of his first three movies and his ongoing support of the project in other media formats, a high level editorial choice to cut that much material from a multi-episode series of books, movies, or TV shows, or in cutting a novel down to another format that allows for less content like a movie, is actually almost the norm, rather than the exception. It tightens the story arc, it reduces the cost budget exposure of whoever if financing the deal, and it reduces subsequent episode attrition in the number of people who consumer the product. If you see an opportunity to do it in advance, you can fix the minor rough spots of the kind noted in the blog post linked that emerge in the overall story when you remove a large chunk of superfluous to the story arc material with relative ease. The lack of tight editing used to be the norm in the publishing industry (ever read Moby Dick or a Dickens novel?), but now tends to be the exception. It is one of those places where creative skill in the editing process has substantial, direct dollars and cents economic impact on the project itself. Rookie writers are particular prone to writing material succeptible to large scale wholesale editorial purging of unnecessary parts of the stories, as they have particular difficulty transitioning from short forms they can get published before they really establish themselves to the beginning, middle and end with more elaboration found in full length works.
This kind of big picture editing, which is incredibly painful, even if you feel better about the finished product afterwards, is every bit as common and necessary in most forms of non-fiction writing as it is in fiction writing.
With better planning Lucas might have done Episode I, if he did it at all, as a pre-pre-prequel and improved the reputation of the overall Star Wars brand in the process, or might have devoted a more or less stand alone sixth episode in the same world that would be more accessible to viewers new to the series that explored parts of the saga explored in other Star Wars properties with proven track records of success promoting cross-selling of Star Wars properties outside the story arc of the core movies.