This is also why hemostatics and (more importantly) tourniquets are great tools in the back country or survival situations. While you probably won't need to be shooting back, you could easily find yourself in a situation where evacuation is a LONG time off and you may be the only person able to provide aid. You may even be the only patient as well as the only care giver. The quicker you stop bleeding the more blood you retain... it really is that simple.
Of course you need to balance how much your carrying vs. what could happen in what your doing. My FAK for wildland firefighing is beefier then the FAK I carry for day hiking.
I agree that not every trauma/bleeder needs a tourniquet. I've never used one.
But, I bet most folks haven't had the same combat conditions, where there isn't just 1 patient at a time, and there isn't an entire ambulance and fire engine team reporting. Usually, it's 1 medic and a crap-load of casaulties happening all at once. He can't spend 5 minutes with each holding pressure, and he can't have the battle buddy do it for him - someone needs to be shooting back.