This read-only value reports the amount of the shared packet-buffer pool currently in use by this Class-of-Service queue on this port (the ifIndex-scoped duplicate of this counter is dellNetFpIfCurrentUsagePerCOS). An admin drills down here, per-CoS, when a port-wide buffer or drop alert fires, to identify which specific traffic class (e.g. a low-priority best-effort queue vs. a latency-sensitive voice/control queue) is actually consuming or exhausting the buffer.