I learned a lot about this subject when prepping my 350Z for STU. Here's a copy/paste from my build thread on my350z:
Corner balancing: I didn't even understand what corner balancing was until I borrowed my club's scales and and spent a weekend in my garage with google and youtube:
My results, with me in the car and 1/2 tank of gas.
Corner balancing is apparently more like "leveling" a dinner table than "balancing" weight distribution. The weight at each corner of a car, on a level surface, is more of an indicator of the suspension's length/height at each corner than an "end" unto itself.
A car with poor corner balancing is similar to 4-legged dinner table that can rock back and forth when two opposing corners' legs are longer than one or both of the other two. But, whereas a table will rock back and forth over the long-legged axis, and alternately lift the two shorter leggs off the ground, making the issue obvious, the springs on a car will keep all four tires in contact with the ground and mask the issue.
The 4 individual scales, and the resulting weights, show how much force each tire is putting on the ground while at rest.
Less force (weight) on a cross-weight (DF+PR vs PF+DR) means one or both of the "table legs" are too short relative to the heavier cross weight. Or, conversely, the heavier cross-weight has a "leg" or "legs" that are to long.
This exercise also showed me how evil sway bar pre-load is. The sway bar tries to make both sides the same and resists any difference between the two sides. So as soon as you sit in the car, the sway bar starts transferring force from one side to the next. After balancing the car without the sway bar connected and then connecting it, I found the sway bar added ~60-70lbs (can't remember exactly) to a single corner once I sat in the car....Now I have adjustable endlinks, which I installed while my weight was in the driver's seat.
*note* a car can have a perfect 50/50 corner balance and not be level. In fact, small rake adjustments made big handling differences on the Z. Fender gap was always a secondary consideration when I setup my coilovers, but I did try to get the left/right fender gaps close to symmetrical without screwing up the cross weights.