In simple terms, they angle the wheels in such a way that under cornering there is increased surface area of the tyre on the road, and therefore more grip.
There is a good explaination here:
http://www.ozebiz.com.au/racetech/theory/align.html
I'm fitting them for track use to improve cornering grip. The angle of the wheel when straight however can cause uneven tyre wear and extreme camber can cause 'interesting' handling. But I'm only aiming for 1.5 degrees, so not extreme, and I don't drive it on the road enough to worry about the tyre wear.
I would imagine using Sportlines to lower a car would create slightly more camber, but only a tiny amount as its only a 30mm drop at most.
For road use, camber bolts are probably not needed.