There is a use case where a user of an app (say: nextcloud) needs to restore a file deleted within the retention period. This is quite dificult right now as the backup feature (or the restore feature thereof) is basically an all or nothing desaster recovery. which overwrites the current state of the app.
You would need to download the backup file from your backup server, decrypt it (optionally) and search for the file.
maybe get some inspiration from duplicacy/duplicati which solves this quite elegantly