[quote name='iiipopes' timestamp='1369712907' post='2091844']
It's not just the string excursion. It's the mechanical impedance of the neck. I have a Gibson J45 which I really enjoy. When I first got it, I was very careful to set it up properly. As I tightened the truss rod to a point of proper relief, it felt really, really good, and it appeared that it could go just a little bit straighter to make the action even better. But that last 1/4 turn of the truss rod damped down the vibration of the entire instrument too much, and the entire instrument lost its resonance. I backed the truss rod back off that 1/4 turn, and all the tone and resonance came back. I left it there, even though the action could, in an abstract sense, be even lower.
[/quote]
This issue seems to matter even on solid bodies but on semis and full acoustics it is crucial.