They don't protect anything. Probably 90% of your catalog is out there on the net and findable with a bit of googling. In the end it's just a bad business decision. You scare away potential customers and your stuff gets pirated anyway. You're degrading your own product and artificially creating a situation where the pirated product is actually a better one (one without a watermark) than the one you are legally selling. You've got to realize how insane that is.