According to those who know way better'n me, (and I quit expecting things that are right to make sense...logic doesn't always follow correctness)
...according to those who know, fletching "corrects" for minor spine differences...influences paradox enough. What you want to do is find how your arrow is shooting "raw". Bare shafts do that and by comparing the fletch POI to the bare POI, you see what "difference" there is between your bow, release and that arrow set up by comparing the bare to fletched impact points.
I shot arrows that were "ok" for many years...but they were on the tail of the standard bell curve of what arrow would work...so under hunting conditions, if I short drew, or was out of position in a stand, I could easily get errant arrows because I didn't have much error margin in my spine set up to start with. Critters deserve better'n that. :(
Using the bare vs. fletched... changing what was needed on BOTH till the bare show slightly.. slightly weak... I found a arrow/bow combo for me that was more in the 'middle' of the bell curve of balance in spine and I had more margin of error for a errant release, etc.
You want a good explanation, Bowmania? Go to OL Adcock's website and read, then print out and re-read several times, his entire tuning guide.
It'll make sense.