This is a simple way to provide some security against dropping your camera whilst carrying when you do not have a wrist strap handy. I use this all the time, it gives me hands free for simple things like opening doors.
There are several ways to make this work. Depending upon the direction of the knot you may tie it so it's loose or even self locking.
This uses a self tightening knot which if used wrongly can cause injury. Don't leave it with a loop in places where children or animals are about. Don't put it around your neck!