> tmpfiles.d snippets can be defined to cleanup on a timer _anything_,
It's a question of what the *default* behaviour should be.
For whatever reason, a lot of people who process large data use
/var/tmp/FOO/ as a place to store information that should not be
backed up, but also should not just disappear.
Maybe they should use ~/FOO/ but put a CACHEDIR.TAG file with the
right magic contents there. Or touch ~/FOO/.nobackup and use duplicity
--exclude-if-present .nobackup. Or ~/.cache/FOO/, although that's a
bit counterintuitive because it's "hidden" and not really meant for
this purpose.
There's a reason people don't want these files below ~/, which is that
some backup mechanisms, like btrfs snapshots or LVMs snapshots, may
snapshot files there regardless; and often /home/ is on more
stable/expensive storage (raid k for k≥1) while /var/tmp/ is on a
cheaper substrate.
Given the era of large data we're living in, this is a ubiquitous
problem. Since we don't give users a standard solution, they've rolled
their own. If we think that solution is wrong, we should (a) make an
actual official suggested location for this sort of material,
/var/scratch/ or /var/scratch/${USER}/ with a link there from
~/Scratch or something, and (b) transition them to it, ideally without
unexpectedly deleting their files and messing up their work in the
process.
