It's poor UI to not name a file on the user's own machine, if they'll ever have to look at it. I'm counting things like web browser caches in this because OmniDiskSweeper/etc users will be seeing the large files you put in there.
Most importantly, APFS is first being rolled out to iOS where this isn't as much of a problem because the user never really sees the filesystem anyway.
It doesn't matter much on iOS, where users rarely if at all have to access the filesystem directly. It is very rare that the same files would be accessed and modified by more than a single application anyway.
