Author has written 20 stories for Final Fantasy VIII, Sailor Moon, Irresponsible Captain Tylor, Reboot, Escaflowne, Psychonauts, CSI, Transformers/Beast Wars, Halo, and Cats.
Fanfiction is not a crime. Anyone on here would agree. People who don't consider writing fanfiction valuable time are sadly misunderstanding the real point of a good fanfic.
Fanfiction, like any writing, is practice. The more people write, the better they become, honing skills otherwise left untrained. The sad fact of the matter is that creating compelling characters and believable worlds is hard to do. Add this to weaving a truly original plot and you've got a monumental task. Fanfic writers merely take what is already provided for them and use it as a stepping stone to higher things. It is a lot like computer animation, an animator must learn how to use action, but may have trouble if they can't build a proper character, so to solve the problem they download prebuilt models to practice with. That's all there is to it... we're practicing with something we love, which brings me to my second point.
Writing a fanfic makes writing fun. All creative writing, whether fan based or original, should be a good time. If its not fun then the readers will notice and get bored. Fanfiction takes a medium that is already adored by the author and uses it to get that person writing their own story. Over time the creativity of the author comes out, creating new characters, places, situations... and eventually that author has enough experience to begin to develop their own universes and their own stories. Some do and some dont, of course, but my point is that fanfiction serves a dual purpose; to teach and entertain.
My fanfiction is for fun. It may not be perfect in spelling or grammar, but I dont really care. I write most my minifics as a lark and the long ones as a passion. As a rule I stay pg13 and try to veer away from romance because its really sappy. I much prefer something exciting or funny to anything angsty or sugary. Of course I am also entitled to violate my own rules from time to time... I have that right, I'm an authoress... I have special powers like that.