This read-only Unsigned32, in bytes, indicates the average size of all messages handled by DRE during encoding (from the LAN side), calculated as a since-last-reset aggregate not tied to a specific connection or peer, and per the description message size is an important factor in DRE performance. An admin uses this to understand the typical granularity of traffic being fed into DRE, since very small average message sizes can reduce optimization efficiency. A drop in average message size over time might explain a corresponding drop in compression ratio, since smaller messages give DRE less redundancy to exploit per operation.