The people on the commentary track talk about how long it took to get a good script revision, what sort of things they had to cut, what worked and what didn't. The deleted scenes clearly warranted deletion -- they didn't fit the theme of the movie, they were unneccesary, or they did nothing to help the story itself. There are pages of poster samples, storyboards for scenes, and production sketches.
As an artist, this is an excellent reminder of how the first try rarely is right, things always need to be revised and changed, even great artists do stupid things in early production, and fine art takes lots of time. When watching a movie the whole thing comes together in under two hours, so it's easy to forget that being an artist it takes more effort than appears on the screen. It's validating, to look at the things I've done wrong, put on the shelf as unattainable, and have on the workbench, and compare that to the similar troubles of artists I admire.