I think many err on the side of overtightening. The freeplay of a loose HS (or any other cup/cone) is relatively easy to detect. It does not take much, maybe a few degrees of adj cone rotation to go from zero preload (my preference) to preload. Preloading cup&cone bearings creates a huge load in itself. Now if you run a tapered roller bearing like some Stronglights, a slight preload is correct. With rollers, the surface area of contact is so much greater that a slight preload will not damage anything.
One sometimes encounters a fork that binds somewhere along its rotation...as previously mentioned due to misaligned steerer, cups or faces. I then simply adjust for best straight-ahead as that's where you'll be most of the time anyway.
In summary: Rollers; slight preload. Ball/Cup/Cone; zero preload/zero freeplay.
Jack Romans
Sacramento, CAlifornia