This reports the number of data buffers currently in use on this node, applicable across all platform types. Trending this alongside the available-buffer count over time reveals whether the node's buffer usage is following a normal, bounded pattern that fluctuates with traffic, or is instead creeping upward over days, which could indicate a buffer leak in the node's software. For example, buffer usage that never falls back down after a traffic spike passes, unlike previous spikes, would suggest a buffer leak rather than normal traffic-driven fluctuation.