Well, just use your judgment.
If it's something you're proud of or that you worked hard on, go ahead and give it its own topic.
If it's something smaller or quicker but still worthwhile, go ahead and group it with other like pieces, either in its own topic, or in a topic dedicated to your own art.
If it's something really small or decidedly not worthy of a new topic, go ahead and post it here.
...Or something like that.
Just don't confine it all to this little topic; there's a whole subforum out there, waiting to be filled with art.