The figure eight knot is often used as a “stop” knot. Unlike an overhand knot that can be almost impossible to untie when it becomes jammed, a figure eight knot is more easily untied if it becomes jammed. Quite often a regular overhand knot will need to be cut in order to free your rope from the jam.
One of the more common uses for a figure eight knot is to attach a rope to a carabiner. This is usually done by tying a double figure eight knot with a loop. This is also one of the strongest knots you can tie when making a loop at the end of a rope. It can be further secured by tying a stop knot on the tag end of your rope.
Staying above the water line!