This sets the peak cell rate for rate queue 6 on this port, the third of the four low-priority queues. With three low-priority queues already available (4 and 5), this third one on this port gives the admin still finer-grained control for isolating another best-effort traffic class sharing the link. A provider running several low-priority customer PVCs across this port might dedicate queue 6 to one specific customer's traffic to bound its impact on the others.