Hi Davide,
first of all, the JPA-File are between ~ 500MB and 12 GB, depending on the frequency we backup (hourly to monthly), i.e. we are using serveral profiles (from "application core" DB tables to full installation). In case we have to restore a backup, we have to keep the downtime as short as possible. Therefore we keep the most recent backups on the local disk of the server since transfer rates to remote storages are not really fast. The next thing is, that the backup files of one profile may also vary a little bit dependend of the usage of the webpage.
Using the quota features of Akeeba Backup makes me feel to loose a little bit of control, because you never know, if a backup is still available locally.
It's be good to have the possibility to tag certain backups in a way that they are not deleted. In other words, it may not always be the case that the oldest backups are deleted.
Perhaps it's the best way for me, just doing a du -sh <outputdir> in a cronjob and let it email to me daily if the query above is not accurate enough.
(Just my thoughts)
Best regards,
Stefan