It’s not uncommon to put several locks on the front door in order to prevent unauthorized entry.
When most people think of their own security, they focus on their front doors. That’s because they go in and out of their front door every day, and the front door is most visible to the outside world,
The security of your locks depends on the status of your keys. If your key is compromised, either because you’ve lost it or too many people have handled it and could have made copies
When all you need to do is worry about a single door lock, only one key is necessary, as only one person needs to have access to your property.
There are times when you want a door to be unlocked without a key, either because you need an unlocking device that is easier to distribute or you would prefer no device to be necessary at all.