In addition to suspension mechanics, wouldn't you make the decision based
on a variety of personal constraints, such as the driver's preference &
desired tire wear (and other factors of human preference)?
As an example using camber, my bimmer specifies about -2 degrees of rear
camber (off hand I don't remember the slop), where I don't corner like a
racer, and I care about tire wear, so I have mine set to as close to 0
degrees camber as the setting will allow.
As another example, I'm not sure what the caster is, but I drive on steep
hilly windy terrain where Xeno has suggested a lowering of caster will help
lower the camber of the inside wheels during tight low-speed cornering,
which, if done within the slop of caster and camber, will result in front
tire wear, which would mean I'd like to be on the low end of that negative
The point of these examples is that personal preferences also can play a
role in the decision as to where to set the alignment when given a range.