here is some analogies of the swing i like. It's a bit late (seems all rapped up), but I'v been busy lately haven't been able to respond.

Its a bit lenghtly but it is so simple yet hard to explain.

Imagine a sling shot on top of an race car. If you pull back that sling shot and release the projectile will go far. If you drive at 100 mph and pull back the sling shot and release it when hitting a certain line in the road, it will go slighly further but not much kinda far. If you drive 100mph and pull back the sling shot and hit a solid steel wall at the same place that line was and release the sling shot the projectile will go flying super far. Now instead of a wall inmage there was a hook on the car that would catch a cable, and instead of that try to imagine the brakes having the stoping power of a cable and hook or steel wall. Just like the faster you stop the further the projectile will go because of the better transfer of potential to kinetic energy), the better brace you have with your left leg, the more potential energy turns into kinetic.

The sling shot is the right arm, the car is the body, and the wall is the left leg or the tires, which contact the ground is the leg (makes it slighly move relevant). The body moves a bit but mostly supports the moving of the right arm, and the left leg is a brace allowing all that momentum and power you have to that "lag" you have built up and once the left leg braces against the ground it release.

Another analogy is the wheels on a car is the left leg and the engine is the right arm and the body is the transmision. It doesn't matter how hard the engine run if there is no trasmision, nor does it matter if you have engine transmision but weak breakes. The transmisions doesn't drive the engine the engine drives the transmision, the transmisions allows the engine to deliver traction and movment. Just like the body allows the right arm to deliver power via the left leg bracing and allowing all that potial energy to release. If you spun your hips out your leg would not be able to brace you very eficiently and all that lets say 100 newtons of potential energy is only allowed to release to 80 and you have 20 newtons left of potential energy that you haven't used.

So many analogies. But all of them show that the left leg is crucial as a brace but itself gives very little power (if that steel wall in the above example moved towards the car you would get a bit more distance. I believe that is why tiger "jumps" at impact so that not only does his right side act as a brace and let all his kinetic energy turn into potential energy, he bouces back a bit and actaully adds a tad more potential energy but not much, kinda of a whipping effect. when you whip a towel you don't just whip it out, you whip it out then pull back a tad. In order to jump back you need to have your hips cleared so I believe that is where people get the whole clearing your hips fast gives you speed, because it does add a little but it is very little and unnesisary) So the leg is a brace and the body (transmision) moving allows the right arm (engine) to deliver power. The body must move in order to allow the right arm a proper path with little resistance, but it doesn't itself add any power but is very nessisary in transmitting power as a transmision is very key to the engine tranferring power to the wheels.

To throw a knockout punch, you first have to step your left leg out with your body and then you brace yourself with your left leg and allow all of that potential energy transfer to kinetic into your fist as it releases into the target. Martial artist do tell you to put your whole body into it, but they don't say punch with you body, they just mean use your body. If you didn't take that step in which I spoke about earlier you would turn you hips to push back and be able to brace yourself and your body moves allowing your fist to go flying into your target. the body adds no power, it allows your fist to travel a much further distance tho. If your arm is 2' long instead of delivering 2' of force, you are delivering 4'-6' or arm pushing because your body it working to support the arm just like in the downswing the body is moving to support the right arm and the leg is moving to support the body. the legs are not moving the body or arm nor is the body moving the arm, the arm is moving itself and the upper body is moving to allow th arm to move the lower body is supporting all of that. that being said the lower body will move first.

Another example is basketball, you don't think of moving the shoulders and then the arm and then the wrist, you think of moving your hands and the arm and shoulder responds to that by moving first to support the hands. just as the lower body moves first in golf, but it is the right hand that is moving the hips and legs unconciously.

hope that wasn't too confusing if anyone is still reading it.