I've always really liked Hal's stuff. However, I wish I could pick his brain and ask him where he thinks one should draw the line between immature and adult musical behaviour. At what point does one stop repetition and work entirely on other forms of practice?
The reason is actually based on the idea of building and maintaining brain-to-hand signal, which he makes a strong case for. A strong brain-to-hand signal is built by repetition. Myelin wrapping is the key and the process can continue through adulthood, though not as efficiently as in childhood.