And aside from reading that in numerous places, that's the way Jimmy Penner set up my coilovers. (14" travel, 16" lower and 14" upper). So I figure if that's the way he does it, then bygawd it's right! Haha.
Those sizes actually fit good on the shock, especially after preloading. After I put the springs on the shock, there were still plenty threads to get the spanner nuts started and run down about an inch before meeting the top spring, so they aren't "too long". Unless I'm wrong, this setup will prevent those that you see with like 5-6"+ of threads showing above top spring once preloaded accordingly, allowing full use of the shock the way it's intended (provided spring rates are correct).
I think most people use too short of springs and go too heavy on spring rates, where as using longer springs, and a little lighter spring rates, and preloaded properly, you get optimal performance due to the progressional spring rates that come after properly preloaded.
I'm still green in the world of coilovers so I may be terribly wrong with that theory, if so, please inform me why, because I like learning...especially if my train of thought is incorrect.