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 an archived historical sample row of that same receive-counter set, kept purely for trending past intervals rather than showing the current live value 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 the endpoint this history row belongs to works out to roughly 200 Mbps of inbound traffic during that window.