Regulation

I'm of the mind that by keeping instruments in tune, you contribute to the general orderliness of the universe. Yes, the idea is as verifiable as the existence of a higher being, but I believe it all the same. At the very least, I can verify that my own mood and musical productivity took a swing up once I got my piano tuned.

In addition to getting it tuned, I had the technician regulate the action. For any non-pianists in the house, this means making a number of refinements that improve the mechanical efficiency of the instrument. When you depress a key, you are not directly forcing the hammer to attack the strings. The energy gets transferred through a few different components before the hammer goes anywhere (if the key and the hammer were attached, holding a key down would instantly dampen the sound). The regulation process gets energy losses to a minimum. Other refinements are also involved, but as I understand it, that's the bulk of it.

In musical terms, this means gaining precise control over dynamics, tone color, phrasing, and all the other nice things that help make a great performance. One other thing I noticed was that I could really feel the interaction of these components under my fingers. Definitely a neat sensation.