This reminded me of one of the funniest or saddest things I have seen lately. When arriving at LHR from LAX last month we saw at least 5 padlocks (some of them were heavy duty Masters type, open but not cut open) floating around our baggage claim carousel. So I guess you can lock it for your peace of mind, but in the long run I think it is better to not to check anything you don't mind losing. (I've had bags disappear totally, but nothing has ever been stolen from a bag I got back)