Become a big enough fan of something - book, movie, TV series and so on - and eventually, you'll want to know more about how it came to be. Behind the scenes stories become a form of entertainment all their own, both part of and separate from the actual thing they produce. With a big enough property, like Star Wars, behind the scenes info from original or secondary sources becomes extremely useful and even vital to those working on various stories and products.
For example, I obviously have insight into the various RPG and miniatures projects I've worked on over the years. Along the way, I might learn something about some other products that are or might also be in development from the same company. When proposing or chasing things that derive from or affect continuity, I might be passed information from other projects beyond the company that influence my own work - though that's pretty rare. When developing my own work, I rely on a variety of official sources, but behind the scenes information can inform aspects of the story, characters, vehicles, and objects that don't make it into the story itself. Knowing who first created a character, or understand the convoluted history of a character name derived from one in the archives can be very useful. It can also prevent using the subject in the wrong way or assigning it the wrong attributes.
With Star Wars, there is no shortage of behind the scenes information, and more is released all the time. Of course, part of that is due to the continuous development and release of new material, but even new stories about the original movies are still coming to light. Some are just interesting stories. Some are educational about how stories are constructed, or how movies and TV shows are really made. Some illustrate the story making process, including discarded drafts or original ideas.
OK, one current project - The Star Wars - literally illustrates an original draft of Star Wars. That's more extreme than normal. Usually, just the original draft might be made available for review.
Behind the scenes info can be found in many forms. Books, blog posts, short or long videos, convention guest panels, and more. For me, my first real behind the scenes feature was a mention in the Making of the Darkstryder Campaign in the back of Endgame. Since then, its been occasional interviews, plus my own endnote contributions on my old Delusions of Grandeur starwars.com blog and some here on this site.
Lately, there has been a surge of behind the scenes stories and source information that gamers and fans might find useful:
For those reading or (hopefully) running my Beyond the Rim adventure for Edge of the Empire, check out the long history of the Wheel article that came out last week on the starwars.com blog. It's part 1, so there is more to come. One of the writers, Abel G. Peña, was one of my co-authors on the Knights of the Old Republic Campaign Guide. Such a summary would have saved me some research time. It totally isn't required for the game - Beyond the Rim has more than enough for the adventure - but GMs who want to delve more into the setting will find useful things to build on. Players could also read it without fear of spoilers - and might find it especially useful if their characters come from the station.
The blog has also started posting bits that were cut from The Essential Guide to Warfare, by Jason Fry. It appears this will be a regular feature for awhile. For those who haven't checked out Warfare, it falls right in line with the Atlas and Chronology and delves into subject and histories affected by war in the Star Wars universe (obviously, it's a lot). As with all of the guides, it has new information as well.
Jason also has a lengthy interview over at Eleven Thirty-Eight about what it's like to work on "non-fiction fiction," and its a great example of behind the scenes. The source material found in all of the editions of the Star Wars RPG falls into that category, and the writers run into similar issues.
Speaking of Jason, author blogs occasionally post behind the scenes stuff. Jason's tumblr is here. Daniel Wallace is another that posts on occasion.
The biggest, most formal work about behind the scenes is the latest in Rinzler's "Making of" series, The Making of Return of the Jedi. These books are great, packed with cool stuff and never before seen pictures and stories.
Of course, behind the scenes info applies to any franchise - just tonight I saw that Wired posted Agent of S.H.I.E.L.D. (yes, I typed the periods) episode 2 easter egges (spolier warning).
Since I've drifted off the subject somewhat, here's another behind the scenes item. Former WEG Star Wars editor, Flash Gordon Zeitgeist and other comics author Eric Trautmann has been doing some layout and design work for the Lady Sabre kickstarter I contributed maps, etc. to. Here's a very small sneak peak for one of the items. Eric was also the editor on the previously noted Endgame book.