That's a can o' worms. I think these days everyone sets the front the same way as the back but the reason for the pillowball suspension is so that the front upper and lower hingepins can be set at different angles so caster changes through the travel, presumably so there's less caster under compression (turn in) and more at extension (stability). The old MBX5 had some caster change unless you put ~1.5mm spacers between the hinge and top plate.