Modern Jive and Tango take opposite approaches in teaching leading. Modern Jive favours waving your hands around and assumes your body will face in roughly the right direction while you do so. Tango favours leading with your body and keeping your hands still.
It's worth considering the finer points of the mechanics of the Tango lead though. Hold your arm straight out and bend your wrist to the left and then to the right. Your hand probably has a total range of motion of about a foot from left to right. Now hold you hand still and move your chest to the left and to the right. You've probably got a range of motion of about 5 feet! This also means that small movements of your chest magnify into larger movements of your hand's position. See how little motion it takes to move your chest to get the equivalent of moving your hand 6 inches to the right or left.
So for steps and pivots, it's possible to lead quite large movements with very small movements from your chest. As your chest only makes small movements you stay fluid, in balance and in control, rather than needing to jerk your arms around, which makes the whole thing feel smoother.
There's a catch. Put a pen in your hand, lock your arm and try to write legibly just by moving your chest. If you want to lead very small, subtle movements, chest leads really aren't the best way to go. At this point it works better to use your hand. (There's a middle ground bit with your shoulder and elbow if you want to think it through). To borrow an analogy from Marc MacYoung, you're posting a letter - your chest gets it to the right town, your elbow to the right street and your hand to the right door.
If you watch / dance with experienced dancers you can see / feel these small subtle movements in their hands and elbows if you're watching for them. A good example is the back boleo to the lead's left. Although the chest lead's the overal motion to pivot the lead will also feel the pressure in their left hand build "like the bamboo leaf bends under the weight of the snow" until there comes a moment where "the clump of snow releases" the energy back into her frame to create the boleo. It can be done just using the chest, but it's a lot harder to catch the right moment. Again watch / feel the left hand of experienced leads and you'll see them do it. It is possible to lead a boleo without this added impulse, in which case you get a more balletic version, but that's most likely down to the follow doing it as an adornment.
However what teachers seem to be concerned about is that if you tell a beginner they can add subtle touches to the lead with their hand, what actually happens is instead they ditch leading with their chest altogether and start sawing their arms wildly around, or use excessive force to cover other mistakes in their lead. So it's better to teach "just lead from the chest" to instill the habit and build up the expertise and then suggest refining it.
There's another catch. It's possible to lead a move properly using this combination of subtle chest / elbow / hand movements and the follow will do exactly what you wanted – and then they'll utter the dread words "Was that what you wanted me to do?". Simply put it was too subtle. "So what?" I hear you ask "As long as she follows what I lead". Um, no; it just annoys them. In this case you actually need to make the lead less subtle. Magnify the movements more until they stop looking puzzled and start smiling. Some tangositas also prefer a more magnified lead as it gives them more energy to do more dramatic ganchos and boleos etc so watch out for their flying heels!
You might also want to consider the compound effects of the movements of your hips, legs and feet to the above. Combine them all and you can lead almost without appearing to move. Hold your hand out and play around with the effect on it's position of making small movements with the different parts of your body. Remember you usually are dealing with movements of inches. Unfortunately these compound effects can also gang up on you to mess up your lead. I suspect a large amount of the seven years it takes to learn how to walk is simply spent learning not to do the wrong thing.
This does mean that while in Modern Jive you have a lot of freedom to do your own thing in a move, especially with footwork, body positioning etc, in tango you really do need to do what the teacher does with their whole body as closely as possible when learning a movement.
Later on when you understand exactly how everything works together, then you can do it your way.
- Christopher O' Shea