The maximum serving capacity of each GGC node, in Gbps, is shown in the ISP Portal assets view. The value is a hard limit on the traffic which can be sent from the node. It depends on the hardware used and the number of machines in the node.
The egress target is a logical limit on the traffic sent from a GGC node to users, in Gbps. It should normally be set to the same value as the Serving Capacity (maximum egress). If you have a capacity limit or bottleneck between the GGC node and users, you may want to temporarily set the egress target to a value lower than maximum.