I use the plastic-wrap services when I travel. TSA can get insist on cutting the bag open and if they do, the wrapping service reseals it. Nobody is going to casually take that stuff off to riffle through your bags and do a quick theft. It also protects you against an overstuffed bag popping the zipper, and further keeps the bag from being scratched all to heck.
I find the extra 10 dollars well worth it for peace of mind.