“What happens is when the branch is pulled down by the weight of the apples, the tree produces a substance (hormone I believe he said) that increases yield. When the tree is young, there is not much fruit to weigh the branch down so they simulate the bending of the branch with these sticks.”
I remember reading something about horizontal branches bearing the fruit. This explains how that works. I will be more attentive to my new apple, which came with 2 horizontal branches. I may weight them to keep them horizontal. As for my older trees, I can try to weight them, but I don’t know if they will give any. I may have to prune the vertical branches this fall.
I think it's just the pulling on the branch that releases the hormones, so it may still work on the more vertical branches anyway. It's worth a shot.