I'm sorry, I was in the military, and we ain't a bunch of Ninjas. We are scared anyway; so yelling comes natural, and you ain't seen nothin' until you see a six foot Marine, yelling and snarling at you. It causes hesitation, and maybe a little puddle at your feet.I have no idea if Army, Navy, Marines, soldiers, Data unit, and Seals yell or scream or if some countries do it and other countries do not.
But the military goal is to shoot before you get seen or hear them coming. I would thing the goal would be different you want to shoot not be seen. You goal is not scare them off but shoot them before they know you are there.