This is a 64-bit high-capacity counter tracking the total number of packets transmitted over the VSL, intended to avoid the wraparound problems a 32-bit counter would face on a high-throughput link. An admin cares because on a busy VSL, the 32-bit equivalent could wrap around too quickly between polls to be useful, so this high-capacity version is the more reliable one for high-speed monitoring. For example, a network management system polling every few minutes on a heavily loaded VSL should use this counter rather than the 32-bit equivalent to avoid missing wraparounds.