In China I came across people who attached sound while performing qigong in parks. They varied from grunts to yelling to singing. Some would stand. Others would connect the sound with movement. Apparently the taoists have many forms of this sort of qigong and its pretty normal for people to be making loud sounds in parks in china all in the name of health.
In xinyi there is the sound of thunder method. The legend has it that mastery of it could hurt an attacker but is lost because training it was so intense. Imagine projecting various shouts for hours on end as part of intense drills. In the end it was abandoned because it was viewed as "lower class people".
I guess times changed but it's pretty clear that when people met on a battlefield the norm was to yell a lot. A war cry had many benefits to it but you dont have to look to hard to see people who want to draw on that extra reserve of power and endurance with a shout. Happpens all the time in gyms & sports.
My view is the xinyi "sound of thunder" method was all about pushing the body past to that next level. Then repeating this again and again. A power method.