This brain research, Cortical activations in primary and secondary motor areas for complex bimanual movements in professional pianists, by researchers Jäncke L, Shah NJ, Peters M. shows that as a pianist's training advances, his or her hands perform with with fewer brain cells being required for the task. In essence, the research describes and illustrates the reduction in cognitive burden as skills are developed in the hands.
The results suggest that the long lasting extensive hand skill training of the pianists leads to greater efficiency which is reflected in a smaller number of active neurons needed to perform given finger movements. This in turn enlarges the possible control capacity for a wide range of movements because more movements, or more 'degrees of freedom', are controllable.In other words, when we develop hand skills, not only are we able to perform those skills with less attention, more processing power is made available for the advancement of further skills. We wonder how so many wonderful things were accomplished by our human predecessors without the mechanical processes we have now. And perhaps at least the start of the answer lies here.
John deal sent this link explaining that children who write by hand learn better than those who type. the article states:
When writing by hand, the movements involved leave an imprint in the part of the brain called the sensorimotor. This process helps to help us recognise letters.
Simply touching and typing on a keyboard produces a different response in the brain, which means it does not strengthen the learning mechanism in the same way.