Watermarks or no watermarks, it's also a rather fault-proof method to protect your works. Ugly as they are but they always work. You only make it easier for art thieves to steal your works without watermarks.
Watermarking may not, either. And it's a real pain looking past watermarks to see the art, meaning even non-thieves have to look at a cruddy watermark distraction. Though, I even use them, depending on the situation. I just don't like them, I guess.