Since I write "Between the Cracks" I would say don't split it up. I dislike genre labels anyway and many of my stories would fall under several labels or none. Besides if you start splitting where do you stop? Where does dark fantasy end and horror begin? What about Magic Realism? Time Travel? SplatterPunk?
I'd say a hindrance, because sometimes it's not so easy to pigeonhole a story. I know the things I write are not neccessarily easy to fit into a genre. On the other hand if the group gets massive and really busy, then it might prove neccessary, so long as you include a "No specified genre" category.