Vertical vs Horizontal Punching

Could someone please explain the benifits of punching with a horizontal fist (elbow up) vs a vertical fist (elbow down)?

Also, when punching horizontally at point do you turn the fist herizontal? At the beginning, middle, or right before impact?

Thanks.

I try to punch so it lands on the knuckles of my pinky, ring and middle fingers. For targets at or above eye level, that usually means a vertical fist. If I'm striking at the mid-section, it's usually a horizontal fist. Anything between those two points gets a fist that's turned at whatever angle makes it more likely to land on the correct knuckles. That's for straight punches. Hooks and shovel hooks are a whole other can of worms.

the point of both kinds is to make sure that your middle knuckle isn't the only point of impact. Both fail enough of the time that you will end up with hand injuries either way

Aren't there any more difinitive answers? Why do boxers almost always throw horizontal punches?

"Why do boxers almost always throw horizontal punches?"

Because they can. Rotating your fist from vertical to horizontal at the moment before impact supplies an additional torquing motion from the shoulder as well as the elbow. The increase in power, and the increased likelihood of improperly landing your knuckles, does not fully translate into increased injury because of the quality of modern gloves and handwraps.

Bareknucklers also rotated their fists at the moment of impact, but their fists turned from palm-up to vertical instead of from vertical to horizontal. The torque was less, supplied as it was primarily from the elbow rather than the shoulder, but they were better able to control the point of impact and lessen the risk of injury to their hands. They also conditioned their hands (sometimes through some bizarre techniques). Seldom does enough detail in the accounts survive to say exactly what their regimen was, but it seems to have resembled in some ways Iron Palm/Iron Fist. In the absence of progressively toughened hands, no punching technique could long forestall damaged metacarpals.