What is the effect of bulkhead shims??

[Nellybobs]

Hi folks, let me pick your brains!!
Im pretty new to the RC scene, im running a zx-5 rtr with an sp upgrade kit fitted, all electrics are standard rtr.
I have been bashing at my local track (Macctrack) a few times and am trying to set my car up correctly, its far from perfect but there is a few things i could do with knowing so i can understand the 'setup'.
Firstly: what effect do the front and rear bulkhead shims have on geometary and handling? also what effect does the 7 degree and 10 degree front yolks have on handling??
Secondley: i see there are different degree front and rear hinge pin braces available for the lazer, do these do the same job as inserting shims? if not what effect do they have??

Cheers people...

Paul.