For me .zip on Windows is equivalent to .tar.gz on Linux - used when I just want to send a folder in a single file very quickly.

Also handy when sending an archive to a weaker machine, that might take a while to unpack a 7z compressed at the highest setting.

.7z is when I want to send a folder encrypted, or heavily compress something to archive (like a database, documents folder, or disk image/iso). It seemingly does the impossible, shaving the size from say 60GB down to 40GB compressed if you use solid mode (which has downsides if there are multiple files in the archive). It’s incredibly flexible, but the defaults are pretty solid for most cases