On the front, standing the Shock up will make the front feel stiffer (as the car rolls) and will decrease steering, but increase damping. Laying the Shock down will make it feel softer (as the car rolls) and increase steering, but decrease damping.
On the rear, standing the Shock up will decrease traction (or add steering), laying it down will increase traction.
As a rule, the more traction the track has, the more you can lay the Shocks down.