Aerobirdbrain

Adding more toe-in on the rear gives you more grip in the rear of the car to a certian point; if you go too far then it just slows you down.

Adding toe-in up front gives you more stable steering when you go into a turn fast and hard, but it will decrease the amount of on-power steering that you'll have while flooring it going out of a turn.

Adding toe-out will do the exact opposite. It will give you more on-power steering coming out of a turn, but it will make the car less stable going into a turn hard and fast.

The nice thing about the "toe-in/out" thing is that it pretty much stays the same for all types of cars or trucks. The only difference is that some cars may react more dramaticaly compared to others.