Exaggerate to make the point...
You have (example) 550mm of space for the spring and its hardware to fit. The purpose of the fork being to suspend stuff..why fill it up with metal tubes that don't do that?
Preload is applied to the spring to keep it 'tight' if you will. Why squeeze it so much? Yes, there is the issue of where in the stroke you want the fork to ride, as the valve body will be sensitive to such positioning. But, if you want to ride higher in the stroke, why not use the correct spring to get you there as opposed to filling the fork tube up with metal?
While others have their point of view, I've never bought any of it. The shants of a longer spring install (mine are 530 instead of the oem 470. Again, why use the fork to hold solid metal when it can hold spring?) of, 'It's heavier,' and 'the motion transfer time will increase,' hold no water in my opinion.
I've used the oem springs, .40 and .42 eibach springs in a 470mm lengths with varying preloads. The .40 XR springs (the longer ones) I use now are so far superior to the others as to be a slam-dunk when it comes to choosing a spring.
AND...the difference in the bike when I changed from 8 to 3mm (on the advice of a local tuner..) was a pretty big deal. Turned the bike into a joy to ride from a non-handling PITA that I was getting fed up with!
If you have the right spring (rate) you won't need 95mm of steel to make up some phony preload number.
.......imo and all that.
Cheers! ;)