It's to keep buffered bytes buffered until the producer is ready for them to be dropped. This is relevant for example for decompression streams which keep a "wi

It's to keep buffered bytes buffered until the producer is ready for them to be dropped. This is relevant for example for decompression streams which keep a "window" of decompressed bytes around to refer to when matching. Of course, the implementation could use an internal ring buffer, but it's more efficient to use the output buffer directly instead.