Chest protection is a feature used to protect/lock your containers from others, it even locks doors. This can be used in any scenario, for example, this offers some sort of protection to people who aren't in towns, or even from your townmates in your town.
It's very simple to use. To protect a container, simply place down a sign on the container and it will automatically lock it with your name on it. For doors, place the sign on the block on top of the door, (the top of the door frame), and it will again automatically lock it.
To add people to your lock, right-click on the sign to select it, and write /blocklocker <line> <name>.