Note how much room for error you have if you come straight up the leg.
I'd also say that the animal is a variable. Deery creatures seem to be impressed with velocity and shrapnel. Bears not so much. The elk I shot last year wasn't real impressed with velocity either. I did the 'come up the leg' thing on him and hit exactly where I was aiming. He still stumbled downhill 75 yards. I'm not sure he would have gone that far had gravity not assisted.
