I don't know for a fact but I think folks started nocking below when tree stands became popular and they would hang their bow while sitting on stands. Years ago I read an archery book and the author described how when he could draw an arrow from his back quiver and put it on the string without looking at the arrow. He'd just slip it on the string and slide it down on the nock indicater. Hunters usually either stalked, still hunted or used ground blinds in those days. It also works well with speed shooting. I like the nocks loose on the string so I couldn't hang an arrow on the string unless I'm holding it.