- writing longhand reinforces several of our key components of memory (tactile and visual)
- long hand writing slows us down, so that we can cogitate in real time on our decisions
- the slower process inculcates the processes involved in our decision of what to write into long-term memory.
- having various and multiple details surrounding a given moment in a score (be they position of the left hand arm/elbow/wrist, timbre, r.h. fingering, l.h. fingering, articulation, etc) all give us a sculptural view of a moment in time or even of a complete phrase. This all leads to a stronger, more complete view of the phrase as 'character', which is ultimately more memorable than any single form of memory alone (e.g. tactile). I often refer to this as the 'NASA technique' or running on all four cylinders of memory rather than one or two or three.
PS Here's the article... please read all before commenting!