I would disagree, files that the user cannot edit or should not edit should not be going into their home directory. Things like cache files should go into a system wide cache directory instead.

Cache files might contain user's sensitive data. Makes sense to keep in them in the user's home directory in those cases.

File permissions?

Isn't that very anti-linux though, to have a directory owned by root but populated with subfolders owned by other users? /home is the only exception I can think of that does this.

Anti-linux I don't know, but it was not uncommon in unices to have home directories in /usr/home.

And there is no written or unwritten rule about that. In fact, /home is a subdirectory of / which is owned by root.

True, but /usr/home is no longer a common place to store home directories. It used to be, particularly in Bell Labs Unix. (Does FreeBSD still do this?)

The Linux Foundation’s File Hierarchy Standard puts user homes in /home, but it’s by no means mandatory.

/home being the *nix home folder directory isn’t written in stone, but plenty of software expects it. Of course you shouldn’t hard code things like that, but that has never stopped anyone from doing it. (Not that we should reward that with de facto standards necessarily.)

I understand the various reasons why a root file system hierarchy isn’t part of the Single UNIX Specification, but it might have been nice.

/tmp

And /run/user

also mail and cron

There's no other path that the user is guaranteed to have write permissions to (except maybe /tmp, I guess).

Why would you want that?

If you have separate partitions, would you really want user data to go to the system partition? Or a third partition?

Do you find having more places that user programs can write a benefit?

I would favor a /var/user/something directory.

The fact that nobody does that is pretty much a consequence of the difficulty of coordinating multiple projects that do not have a common authority, not because it is a bad idea.

Again, what do you prefer about that?

Maybe the reason no one does that is simply that no one shares your preference.

Having a clear separation between actual user data files / documents and stuff like cache for different reasons:

- easier to cleanup/wipe without risking deleting works/personnal files

- backup solution doesn't have to have a town of entries in an ignore/exclude file

- same as above for syncing software

- tier storage separation possibility

- disk space allocation separation depending on data vs volatile stuff

Should that count towards user disk quota?

I agree cache file should not go into their home directory, however I don't agree they aren't user data and that they would be part of the software installation.

If I uninstall ssh I still want to have have my authorized hosts. If I uninstall some firefox version firefox I want to keep my profiles. XDG defines a thumbnailing hierarchy followed by multiple libraries, uninstalling any of those shouldn't clear thumbnail caches.

Persistent user-specific state needs to live in a persistent user-specific location. You could choose not to use the concept of a home directory, but you would be doomed to reinvent it.