I have used UPX on Windows some 15 years ago and liked it a lot these days. My primary motivation was not network transfer speed, it was HDD storage, bandwidth, and especially latency. It was faster to sequentially read the complete binary, compared to reading individual memory pages as required.

Nowadays disk space is very cheap, disks are often solid state with ridiculously high IOPS, but antivirus software became much worse and likely to mark a UPX compressed binary as malware.