I remember in an interview with Eric Mona, he talked about getting paid from the distributors some nine MONTHS after shipping. Think of the costs there in terms of interest alone. Right there, that's about 4% on your money.
To be clear, that was for the notoriously corrupt, mob-run magazine business. Book publishing is not quite so screwed up, and the payments are much, much faster to the point where it really isn't a problem at all.
--Erik