In my experience, repeatedly shouting at someone to do something is the worst way to get compliance. The WORST. Children, adults, mentally stressed, drunks, no matter what. Danger met by shouting and screeching escalates the danger.
When I looked out my window and saw a coyote standing 40 feet from my children reading on a blanket in the yard, I knew if I shouted, they would spend time trying to figure out wtf was going on. Instead, the safe solution was to calmly say, "kids, do not ask any questions. Do not take anything with you. Stand up and start walking toward me. Don't pick anything up, do not ask questions, I will explain when you get here. Get up and come toward me." And they could tell something was very wrong, but that ACTION was needed before thinking. Because they could process it. Because I wasn't shouting 3-word repeats at them.
Similarly when I've chaperoned and had kids get an injury or a panic attack or a medical emergency. If you want them to do something, ask CALMLY. "You need to sit right down there, I'll work with you. You sit down and I'll come to you. You, get the medical bag. You, give me your tee shirt." If I screamed "GET THE BAG! GET THE BAG! GET THE BAG!" I would not be able to address the emergency.
Why cops do this stupid military screeching bullshit is entirely beyond me. It works for NO ONE. It's confusing and hard to understand. There is no way for them to hear him say, "I'm getting down," because the cops won't stop screeching. It's dangerous. It escalates everything.