This Counter64 is the number of bytes received on this endpoint just since the previous poll, i.e. the increment UCS Manager already computed rather than the raw cumulative total. It matters on the live receive-side counter set UCS Manager keeps for one Ethernet endpoint (a blade's vNIC adapter port, an I/O Module uplink, or a fabric-interconnect server port) inside a UCS domain because it is the field a dashboard can graph directly as a receive-throughput trend without having to subtract successive totalBytes readings itself. A totalBytesDelta of 750,000,000 over a 30-second interval on this interface works out to roughly 200 Mbps of inbound traffic during that window.