We used them as the starter knot before lashing someone down on a stretcher before carrying them out of a disaster zone. It was quite fun, putting the stretcher up on its end or turning it upside down to demonstrate how well protected someone is once lashed to a stretcher.
I like the effort and organisation of the website though, so I'm not knocking it, just pointing out it could be improved with video's that show 1st and 3rd person perspective of hands tying knots. That way, when abseiling, rock climbing or doing other Fred Dibnah style activities, you know if your knots have been tied properly or not.
So much trust is placed on people who run these activities, its nice to have piece of mind, but its probably one of the reasons why the carabiner was invented.