In Weight Placement and Pivoting -- Part 2, I wrote:
"If you pivoted on the balls of your feet, you will now be to the left of the line. If you pivoted on your heels, you will now be to the right of the line. Either way, you are no longer on the line. Your body has shifted.I thought of an example to demonstrate this. Imagine that as you step forward (either shifting slightly to the right or left of the line), you hold a spinning gyroscope near your stomach (hara area). If you move straight ahead, you will not feel the gyroscope pulling you either to the left (as you move right) or to the right (as you move left). Remember that the gyroscope resists in the opposite direction of your movement.
Now that is OK if you intended to shift, but if you did not, what happened?
Either way (shifting to the left or right of the line) it took energy to move off the line. It would have been more efficient to move straight on the line."
The gyroscope will also resist your forward movement, but this would happen whether you moved straight ahead, or ahead and from side to side.
If the gyroscope resists side to side movement, your body is obviously subject to some resistance as you do this. It is more efficient to move straight ahead.
There is a saying in bojutsu that you should hide behind your weapon. I first heard this from Sensei Toshihiro Oshiro, but the same applies in weapon arts such as sword and spear. As you face your opponent, the point of your bo (sword or spear) should be aimed directly at his centerline. If he moves toward you, he will be stabbed by the point. To attack your centerline, he will have to deal with your point first.
The same principle applies in empty hand arts (you should hide behind your block or strike). When you move from side to side while advancing, you are changing this line of protection and attack. A skilled opponent could exploit this.
Of course, lateral movement may be used to avoid or slip an attack. If this is the intention, then such a movement makes sense. But you should not move from side to side unless you intend it.
Otherwise, there will be inefficiency and resistance.
Charles C. Goodin