I personally think it's a fun project. If you like Star Wars but felt that Anakin should have, say, called himself Darth Xader instead of Darth Vader, you can write a funny AU where Darth Xader exists or whatever. But not for serious writing. EXAMPLE:I wrote a CHERUB Fanfiction where all of the criminals James' had caught figured out he was the spy and came after him while he was at university. It was fun doing all that and imagining what James would do, but it was silly and I don't regard it as real work.