More than one lock on a door can make it more difficult for intruders to get in. Whether you have a lock set, dead bolt or security chain, it's even more important to be mindful of who has access to your keys and home.
Instead of giving your babysitter and dog walker all of your house keys, give them one key to the front door or the garage door opener. That way, if the babysitter's key is lost or falls into the wrong hands, a burglar won't have access to the other locks on the front door or any other doors.
The same goes for handing out keys to the valet attendant and car mechanic. With a little foresight, it can be easy to minimize risk.