Also, depending on the system, you could mint a copy of your key that can only access part of your locker. If your friend is really good at fooing widgets, you

Also, depending on the system, you could mint a copy of your key that can only access part of your locker. If your friend is really good at fooing widgets, you don't want to do it yourself, and you don't want to continually bring all of your heavy widgets to them, then you can make a copy of your key that can only access the part of your locker holding your widgets and give that to them so they can come by and foo your widgets for you. With this system, you don't have to trust your friend to not mess with the other contents of your locker. You don't have to trust them to not take the money or personal documents you have in the other part of your locker. Maybe you believe you fully trust this friend, but maybe you don't fully trust their key-handling. If you gave them a restricted key, and you think one of your personal documents is missing from your locker one day, then you can skip worrying about whether it was your friend that's responsible. If your friend loses their key one day (they misplaced it, or someone stole it from them), then you don't need to freak out and worry about your personal documents; it's only your widgets that are in danger. If someone knows that your friend is given a lot of unrestricted keys to people's lockers, they might be incentivized to try to steal/blackmail/threaten the friend for their keys so they can get to people's important documents; if it's known that the friend always requests restricted keys from people to foo their widgets, then an attacker who doesn't care about widgets isn't incentivized to try to attack the friend.