It works the same way as having lots of front camber, the more camber you have (up to a point) the more grip you gain...
from factory 80 percent of cars are designed to understeer, so the easiest way around this problem is to take grip away from the rear... by reducing the amount of camber
or you could flare the front arches and make a wide track hub and wishbone setup to make use of the rear camber
Clio cup cars are a good example of this, you can see how upright the rear wheels are (and how much toe out some of them run) just to get the front to point where they want it to...
It makes sense when you drive them