Didier:
...
>     I would say that having such a directory available is very
> convenient, if the user has write paemission on it. /run is mounted on
> tmpfs and is a very apropriate place to put small short duration files,
> rather than on the SD card.

Isn't that what /tmp and /var/tmp is for ?
And if /tmp doesn't suffice, nothing hinders the local
admin to set TMPDIR so something suitable for his/hers users.

Regards,
/Karl Hammar