@LFJ --I'm not sure exactly what
leading with the wrist means, or how that leads to tan-da or crossing center. I'd welcome clarification here.
As far as proper elbow position and energy, ...yes I
do see that as essential, and how it allows a sort of dual functioning of simultaneous offense and defense with the same arm. IMO
that is good VT.
I mean having your mind at the hand, rather than back at the elbow. Of course, in fighting it should be a non-thinking habit, but if you don't train this way from the beginning (SNT), then such a habit won't be developed.
If your mind is at the hands, you will need one to defend while the other strikes, or defend then strike with the same hand in two beats, because there is no elbow idea.
If at the elbow, the same arm can perform both functions of
taan-da. Like pole fighting, the shaft displaces obstructions, the tip is for striking.
As far as crossing center, if your mind is at the hand this can happen easily. Take
jam-sau for example, at high speed, high stress, if you react to a feint with the hand it's quite easy to overshoot, crossing the line or dropping the hand, losing counterstrike alignment and opening your center.
If instead you are leading with the elbow, there is a built-in safety from this. Your elbow can't physically cross your own center, and your "gun" will still be aimed at the target. So, whether you react to a feint or not, you're still in good position to attack/defend.
This is in part why we place so much emphasis on the elbow. The built-in, non-thinking defense is almost foolproof. We can maintain our clear striking zone without having to think about how and when to block with which hand.
Many don't train with this idea. In
daan-chi-sau practice, many first block down or back with
jat-sau or
jam-sau at the wrist, and then punch. Many ideas while the one little idea is missing.