This read-only Counter64 counts the bytes this PM instance successfully forwarded out on egress. Admins trend this against the interface's provisioned bandwidth to see how close the service is running to its ceiling, since forwarded bytes — not accepted bytes — reflect what actually left the box; because it is drawn from the grand-total statistics bin for this PM instance, it aggregates across the whole PM instance rather than any single rotating window, so it's the number to cite for a service's overall lifetime performance rather than its behavior in one interval. On a 100 Mbps residential broadband EFP, this might read 6,340,000 bytes over the current statistics window — a number an admin would divide by the bin length to sanity-check it against the port's 100,000,000-bps ceiling.