Maintaining equilibrium in the hand.
Any finger of a hand can act as an anchor to stabilize the motion of any other finger in the same hand.
Example: a C Major scale upwards in the right hand.
When I’m on the E with my third finger, I let the third finger “take root” on the keyboard, anchor-like, so the muscles in that finger, and in it alone, can act to raise the thumb, move it to the right, and then lower it down back onto the F. By doing so I never lose, even for a split second, the balance and equilibrium in the hand.
Example: a C Major arpeggio downwards in the right hand.
When I’m on the C with my thumb, I let the thumb “take root” on the keyboard, anchor-like, and use the muscles in that finger alone to lift up the entire hand (like the arms doing a ‘push up’), draw the third finger over it, and place the third finger on the G. Once again the advantage in this procedure is that there is not a moment during the passing over of the third finger that throws my hand out of equilibrium.
I am not advocating using this anchoring system in every chord or arpeggio, only when the stability of the hand needs to be maintained throughout the course of a sudden gesture.
In principle, every time we use one finger and then another, there is the potential, if we so choose, to use the first of the fingers to anchor the motion of the next finger until it is on its note. This next finger, once it has settled down on its note, can in turn become an anchor for the next finger to play. And so on.