This buffering would decouple whether the sink is keeping up from backpressure on RangeFeed. If the buffers fill up, then the RangeFeeds would be temporarily shut down while it empties out before being started up again. This would possibly help with stability in the face of a degraded (but not totally down) sink. The RFC describes the --max-changefeed-memory and --max-disk-changefeed-storage flags which put a limit on how much buffering happens.