The essence of the problem is that there's no standard pathname for a personal directory that's guaranteed to be on local disk, even if $HOME isn't. Consequently, people have relied on /var/tmp/$USER for this. There are realistically affected users who can't change the new defaults.

Cleaning up /var/tmp on a timer is relevant to this academic environment (desktop-based research computing):

1. Each Debian machine is used by only one graduate student, but students do not have root access.

2. Today, /var/tmp is the only persistent local directory where the student has write access ($HOME is on a network filesystem backed up by the university).

3. Within the student population, there is strong institutional memory that /var/tmp isn't backed up by the university and isn't extremely robust (e.g., RAID), but also that nothing there is automatically deleted.

4. Students use /var/tmp for hundreds of Gb of data from simulations that take days or weeks. $HOME is too small and too slow for this.

5. In practice, less than 1% of students lose data through disk failure, accidents, etc.

6. A much larger fraction of students will lose data when sysadmins, who didn't get the memo about the /var/tmp change and thus haven't addressed the ingrained institutional memory, deploy new Debian machines.

7. Some of the students who lose data won't graduate on time.