I have a backup from a ten episode TV show. Open the Package Contents, and I see 4 folder and 4 files.
The files, backupinfo.plist, flexolibrary, currentversion.plist, settings.plist all ad up to 475 KB.
AsyncCopy folder has one plist file that's 2 KB.
Motion Templates folder only has reference folders that are all empty.
Season 1 Event folder has folders for each Project, each of those only has a current version file. All of those add up to 39.5 MB.
The other two folders are Events that are pretty much the same, adds up to 5.6MB.
So my total backup library is only 44.7 MB according to the Finder.
The actual working Library is 1.79 TB.
Side Note; Only one Event for Episodes. One folder for each Episode, populated with keyframes and smart collections pertaining to that specific episode. This show cross references media in other episodes constantly. It's an educational series. In this specific case the media management system works. In other shows I produce or edit, we have an event for each episode.
The backup library is ONLY databases and reference folders. No actual media or cache files exist in it. If you have the original media to reference, you can open a backup, relink, let the cache and proxies repopulate, and you're good.
BUT most smart editors have a separate backup drive and run Time Machine or Carbon Copy Cloner or something to do nightly backups of the whole thing, media and all.
Warning, I have twice seen one or two backup libraries not work. Both times because they were backing up a working library that was already corrupted.