You are right that the concept of a backup is something different from what you are expecting: that the result would be an identical and immediately useable copy of your media files.
A backup is always the first part of a two steps process: backup then restore.
For instance you can use a zipping utility to backup a folder hierarchy. You get a compressed .zip file which is not useable unless you unzip (decompress, that is restore to the original state).
As Greg correctly points out, the organizer is an asset manager built on a powerful database engine which records, indexes all kind of info about your files.
The catalog itself is technically a folder containing the main database and its accessory tools and folders. It also holds a cache for your thumbnails (another sqlite database). The structure of your folders hierarchy is necessarily recorded in the catalog (folder).
The backup is also a folder, containing all the components of your catalog folder and renamed copies of all your photos and videos. It also contains a special file (backup.tly) which is another way to translate the folder organization for the restore process.
Tip: that backup.tly file is the last one recorded in the backup process. If it's lacking, that means that the backup was not correctly completed.
The purpose of the backup / restore process is mainly to solve two kinds of problems:
- the computer crached, was stolen...
- or more frequently, you want to transfer your library, photo and catalog to a new hardware.
To perform the transfer, you must obviously store the contents of both the catalog and the catalog; You must also update the location of each media file in the catalog database to the new location (new computer, new disk/partition or new master folder).
Usual general use backup solutions can provide backups separately for the media and the catalog. They can't update the location information when you move to another disk or location.
Side note:
The other Adobe application also based on a catalog, Lightroom Classic, does not provide backup for the media files (photos and videos), only for the catalogs. You are supposed to choose your own way with other softwares. To update the contents of the database, you must have a simple folder hierarchy. Then a reconnection process is available for the database. The reconnection feature in Elements organizer is not practical to do the same, you have to backup and restore from the organizer.
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