@TomJoad71 wrote:
For the files in my laptop hard disk that are saved and synchronized directly under the Dropx box folder, my impression is that a backup doesn't make sense ...
That's more or less correct. The two functions, sync and backup, serve two purposes. If your files are already in your local Dropbox folder, they're syncing to your account in the cloud and you have some protection for lost or damaged files (version history, file recovery, Rewind, etc.). This isn't a backup, though. The files can be accessed in the cloud or on other devices. It's purely a sync.
Backup is meant for those files that don't exist in your local Dropbox folder and can't sync. Files like those in your key folders (Desktop, Documents, etc.) and external drives can be backed up to your account. These backups are stored separately and cannot be accessed like your regular files. They're simply stored online and are available to download should the originals become lost or damaged.
That being said, you should still back up the files in your local Dropbox folder if they're important to you. This would be done by occasionally copying them to an external drive, using a third-party backup software, etc. Cloud storage is great, regardless of which service you use, but mistakes happen. For instance, you may accidentally delete a file and not realize it until after your recovery period has passed. If you keep your own backups as well, file recovery becomes much easier for the things that Dropbox can't recover for you.
