Well, if you are running a fully cambered ski, that is alot of edge to move around. It can be quite grabby when your least expecting it, which leads to poor ride quality and higher risk of injury (particularly in the knee). An early rise ski (ie camber underfoot, rocker tip/tail) will be slightly more forgiving when those twisting motions happen. They are also much more cohesive to press and butter even in sketchy conditions.
Riding an early rise ski feels like the ski is working for you, were as camber makes you work against it.