The APFS feature that I'm having the most trouble with is 'purgeable' space. It's extremely not clear when it purges or if it matters whether it's a user-visible application or a unix-y utility like cp consuming space. I seem to be able to run out of disk space and have problems when 100s of GBs are supposedly purgeable. There are CLI commands to purge space, but it's also unclear from the man pages what the parameters are supposed to be to get it to do the thing.