I think that it's more useful to think of all defenses against physical intrusion as increasing the cost of intrusion in some way, be that time, skill, risk of being caught, access to specialized devices, etc.

Most "normal" locks don't increase the cost too much but they do raise it - perhaps enough for a thief to pick another target, or perhaps enough for the thief to choose another method of entry such as kicking in the door (which itself comes with additional risk of detection).