Trauma is not just caused by gun shot, think car accident, gas explosion, falls, chain saw, etc. A simple fall on a trail can produce a penetrating wound and collapsed lung or sucking chest wound.

If pressure is dispersed, then it will not work. It is actually surprising how much pressure it takes to stem arterial bleeding. Some people may need to place most of their body weight on the wound, directly on it. What is described by Tjin is more for cuts that do not produce massive bleeding.

While my experience may not be normal (at least I hope it isn't), it has taught that you can keep a person alive in spite of massive trauma. It does involve learning how to do it. I highly recommend the Wilderness First Aid course, wherever you can get it. It is not only taught by the National Outdoor Leader School (NOLS), though they may be the best. It is focused on dealing with a wide variety of injuries and illnesses where help may take some time to get to you.

In spite of all of the training I have had, experience tells me that I always need to plan for communications and trying to get help with evacuating the casualty. First aid, especially in trauma cases, is only to keep them alive until more help arrives or you can get them out. Deep in a canyon with no roads in the Summer, even a sprained ankle can be catastrophic in certain circumstances.