Empire v goblins, empire, bretonians, DoW, lizards, mortals of chaos, dwarves - all would benefit from the 6+ save in most cases
6+ is an infinite improvement over no save.
5+ is a one in 6 improvment over 6+
etc.
I am not saying make it compulsory, just optional at +1 point, you dont need to take, it, I always would.