Think about what happens when you're making a left turn at a high speed -- the left side of the vehicle seems to lift slightly, and the weight shifts to the right side. In physics, this is called centrifugal force. We can feel how the distribution of weight gets exaggerated on the right side and relieved from the left side.
Let's look at how cross-weight affects handling in NASCAR races. When a race car makes a left turn at a very high speed, this weight shift to the right can dramatically affect any uneven cross-weight that exists. Consider what happens when a race car enters a left turn at a high speed with decreased wedge -- where the left-front and right-rear have more weight than the other two. The left turn evens out the difference in the weight on the two front wheels but intensifies the disparity in weight on the rear wheels. The rear wheels then don't grip as well as the front wheels, which can cause the rear to swing out (oversteering).
The reverse happens when a race car enters a left turn with increased wedge -- where the left-rear and right-front wheels have more weight than the other two. The left turn evens out the difference in the weight on the rear wheels but exacerbates the disparity in weight on the front wheels. The front wheels then don't grip as well as the rear wheels, which can cause the vehicle to push forward despite the turn (understeering). However, the advantage to increased wedge is that it can give the driver more control when coming out of a turn.
So, how does this relate to real-life racing situations? Find out how pit crews adjust the suspension and weight distribution of the race car in the middle of a race.