Last September, I wrote a big post on the blog about how to define fan fiction. This week, io9 came up with another category of fic (Be warned: the link is about specifically racy fic, so if your boss has trouble with images of Kirk and Spock in a clinch, you might want to wait to click. That, or move to DC, where you can work from home and click to your hearts desire since apparently none of us are ever getting into the office ever again.), or perhaps another use of it that I should have considered: as a training ground for professional writers, or as a space where they can play with prose and plot a bit by toying with someone else's characters. In that sense, fan fiction is like any other writing exercise professionals use to keep limber. It can be exhausting having to design plausible characters if all you want to try to do is improve your writing of tense dialogue, or your description in a sex scene, just as it can be tiring to come up with an concept to support a full-length article when what I really want to do is play around with a small idea, or come up with a better way of structuring a single argument rather than a web of them.
I'm glad fic is no longer so stigmatized as to prevent talented writers who started out in the genre from making the leap to the big time. It would be a tragedy if, say, Cassandra Clare hadn't gotten published simply because she mashed up Adrian Mole and Lord of the Rings. And apparently without fan fiction, we wouldn't have Cordelia's Honor, either. We should thank our lucky stars, and authors' dirty minds.