Hmm - I guess I don't have to worry as much about losing the keys to my trailer hitch lock! Just gotta remember to pack my spare key, aka the crowbar.
I agree with fastpat (scary thought). Locks won't deter a pro. But if a hack sees two opportunities, and one has a lock, while the other doesn't, he's going to take the path of least resistance. And actually, so will the pro in many cases.
-Z-man.