Prusa/Mendal Z axis

I'm curious, anyone have thought on what are the advantages/disadv. of having threaded rod on outside vs inside? Kinda hard to explain, but if you look at the Prusa I3:

Prusa I3:



You can see the Z axis threaded rod on the "inside" of the x axis, vs the opposite:

Mendel 90:



any thoughts either way ?

Edited 1 time(s). Last edit at 05/09/2015 12:29PM by thetazzbot.