This PerfCounter64 counts Bytes Random Early Discard, Dropped by a QoS Shaper in the current bin, i.e. bytes proactively dropped by the RED congestion-avoidance algorithm before the queue actually filled. An admin watches live RED drop bytes to see whether the shaper's congestion-avoidance tuning is discarding traffic prematurely, which can hurt throughput even before a hard queue-full condition occurs. If f3FpQosShaperStatsBREDD climbs even while the shaper's queue isn't full, the admin would consider relaxing the RED thresholds so TCP flows aren't penalized before true congestion sets in.