Guy:
flowerchild: but I also seem to reuse characters, so when you come to know the characters, shorter stories are easier.
Well yes but...
For a contest entry is it really safe to assume that the reader is already familar with your characters? One of the advantages of this particular contest format (no author names) is to put all authors, new and well-known, on equal ground. This "blind" format serves to encourage both readers and writers to explore new territory
Well, if it's a fanfiction story then the writer might assume that the reader has (or could acquire) some of the basic background if knowing it were necessary to understanding the story. Beyond that, however, IMHO even a fanfiction story should be self-contained--while the author might state that this story occurs near the end of THE TWO TOWERS, for example, the reader shouldn't have to read (or reread) that part of the book in order to make sense of the story.
Reusing characters shouldn't be a problem of and by itself, but I'd venture that a contest entry still should be self-contained in that a reader shouldn't have to have read earlier stories to make sense of that particular one. OTOH, merely because the characters have been used in other stories wouldn't mean that a story necessarily isn't self-contained--a story may relate to earlier stories but still effectively stand alone on its own merits, I'd venture.
For a regular posted spanking story (not a contest entry), obviously it would be up to the writer as to how much background RE his/her previous stories he/she decides to assume the readers has... --C.K.