How you decide on where the load goes is really dependent on the aircraft type and the structural limitations, you also have to consider fuel burn as well.
When I'm doing my plans I like to think of a pyramid centered over the wings. That's where the heaviest stuff tends to go because you have the strongest strucuture underneath. Then you work out from there.
For the MD-11F we plan them nose heavy because our MDs have tail tanks which exerts a substantial aft moment, but then it does go away because it's all fuel. For the 747s I do it just the opposite and have them slightly tail heavy because the fuel loaded exerts a forward moment.
The whole point is to get the aircraft as balanced as possible for several reasons but these 2 really come to mind: if the load plan is very balanced if something breaks loose the effect of the movement is minimized. Also, the closer to balance you are you fuel burn seems to be better and the aircraft is easier to control.
Just my two bits.
BTW, if you have any additional questions mail me.
is that a light at the end of the tunnel or just a train?