I was referring to the flatter trajectory of downward shots (in close), compared to a more horizontal one. There is less gravitational pull as you shoot more vertical. I guess with modern bows having incredibly flat trajectory to beginwith, this might not be a concern. An extreme downward (straight down) shot is something you want to avoid on an animal, I know. They can be done, but not a good idea, nonetheless.
The poster brought it up, so from tree height, what else could he be referring to? Maybe he hunts from the ground, but that wasn't mentioned.