I think in such a category, one would, let's say, post a first attempt at a form new to them. Thus, one who has never composed a fugue or a sonata and knows that they have room for much improvement, but has still composed a first attempt at it for which one would like to receive some feedback can post it there. In this way, this new category labeled "exercise pieces" or "draft pieces" will prevent the beginner from being judged for his/her first attempts at a form new to them as though they were submitted as final products (as they would be, or be perceived as, in the other categories), and thereby allow them the possibility of improving. It will also encourage one who has so far stuck to their limited style to dare to experiment and get out of their comfort zone but in the "safe" area of the "exercise" category.