[qrmn]

I can't think of many scenarios in which this would be a win which aren't usually compressed archive downloads of some sort anyway, or might be better presented as a torrent with a tree hash and some multisourcing.

LZ4 might be a better choice. It compresses moderately well, but the packing and depacking speed are much better. Has anyone investigated whether it's viable?

Also don't forget that you need to be careful about compression in a few contexts where attacker-injected data and a secret could share a compression context (the BREACH attack, for example). Compression is usually a good idea, but you should really salt new CSRF tokens every load. HTTP/2's header compression is context-free to mitigate the related CRIME attack.