Moving the Steering Spindle Up and Down changes two things:

It changes the Total down travel your front end has. More Down travel in the front will give you more predictable landing off of jumps. It will also give you less steering as you exit the corner on power. Less Down Travel in the front will make your car less predictable landing off of jumps, such as sticking into the dirt like a lawn dart if you land extremely nose down. The advantage of less down travel is increased corner exiting steering when you are on power. I like to use this adjustment to quickly see if increasing or decreasing the downtravel in my shocks will provide the corner handling that I desire.
Thespindle height will also change the amount of bump steer your car has. Lowering the spindle will give the front end more Bump-In. Raising the spindle will give the front end more Bump-Out. This is if you do not add or take out any washers under the steering ball end. Bump-In will give you more steering entering and through the corner. It will also make your car feel more aggressive to initial steering inputs. Bump-Out will give you less steering entering the corner but more through and exiting the corner. So in high speed sweepers Bump-Out will give you a more consistent steering “Feel”. Bump-Out will also dull some of the initial steering inputs. I personally like to use Zero bump in or out. So if I change the height of the spindle I have to add or subtract shims from under the ball end to keep the Bump at Zero.

The "Spindles" are what your front tires attach to. You can change the height of the spindle and this mainly changes your corner exiting steering. If you need more steering as you exit the corner, you can raise the spindles (Two washers on the bottom). If you need less steering as you exit the corner, you can lower the spindles (Two washers on the top). Just make sure that you add or remove bump steering spacers as you raise or lower the spindles. This will keep your bump steer the same.