Once the traffic is mapped against a forwarding class, the discard probability for the traffic can be configured as high or low priority at ingress. Once the traffic is further classified as high or low priority, different congestion management schemes could be applied based on this priority. For example WRED curves can then be run against the high- and low-priority traffic separately, as described in Slope Policies (WRED and RED).
This ability to specify the discard probability is very significant because it controls the amount of traffic that is discarded under congestion or high usage. If you know the characteristics of your traffic, particularly the burst characteristics, the ability to change the discard probability can be used to great advantage. The objective is to customize the properties of the random discard functionality such that the minimal amount of data is discarded.