If you use the same scales, grip will be slightly thinner toward the rear with a tapered tang. Can help make a slightly lighter, more lively knife.
It will move the balance of the knife forward. My tapered tang KE Bushie balances perfectly on my index finger right at the base of the scale where it meets the finger guard - which is right where I want it.
I didn't try a non-tapered version, but I imagine it would feel slightly handle-heavy.
Perusing the Fiddleback posts from 2012, I can't decide which looks better to me - tapered, or full thickness. WIth the way he lays up his scales, liners, pinstripes, and pins I think both options look absolutely fantastic.
Mostly, I think it is difficult to grind an evenly tapered tang. Doing so, and perfectly mounting the scales, shows Andy's skill as a knifemaker and meets or exceeds the expectations of an ever more hard-to-please buying public.