Assuming that the ear is alert and that the hand functions well the only reason to practice is to reduce the time it takes to register one's response to the quality of every tone as it flits past, faster than any speed that we can consciously register.
It is a speed of animal alertness, accessible to urban humans only under special circumstances, like a superb live performance.
Without that alertness practice becomes routine, counterproductive. Maintaining that alertness also requires practice, but of a not-repetitive sort: that is, paying attention to our vivid response to every sound, either liking it or rejecting it. Most practice is associated with dulling that response by constant repetition of same-old, same-old.
I think of playing the piano as chasing vibrations.
