I would have thought the benefit was obvious. User choice. I can choose to clear the default backups at my own choosing.
The problem with backing up directly to an external hard drive is that they are more prone to failure than internal hard drives. I speak from experience.
If you set preferences to always back up to an external drive, you would be better to keep an extra copy on another external drive, a DVD disk or thumb drive. Then you won’t be left high and dry.
Lightroom has always been designed to provide “double indemnity” which is why users can save metadata to file/XMP in addition to the catalog.
