This is a 64-bit high-capacity counter tracking the total number of transmit errors on the VSL, avoiding the wraparound limits of a 32-bit counter under sustained high error rates. An admin cares because it's the more dependable choice for long-interval error-rate trending on a high-throughput VSL where the 32-bit counter might roll over between polls. For example, trending this counter over a full day on a high-traffic VSL gives an accurate cumulative error count that a 32-bit counter might have undercounted due to wraparound.