I have been travelling to USA and various places around Europe for the last 16 years. I use the TSA locks and have never had an issue, either with my case being opened, or the locks being broken. To me its like a PP poster said, its a deterrent for opportunist thieves. I know that the bags once behind the scenes before they get to the planes can be tampered with at any time. My reasoning is , at least with the TSA locks, its harder to tamper with. Also, having a TSA lock or zip lock on bags means the zips are less likely to get caught and get ripped open as the bags trundle along the miles of conveyor belts in the airports.