How does the secret save backup feature in Pokemon Sword/Shield work?

Recently I was researching save management in Pokemon Sword/Shield, hoping that the Switch release of the game would finally allow for multiple saves to be created.

Sadly it was not the case (you can use multiple users but if you want to go online every one needs a separate Nintendo Account), but while I was collecting info I came upon an interesting thing about an hidden feature of the game.

By pressing UP, X and B at the same time at the title screen, one can access a second "backup" save slot. I tested the code myself to be sure, and indeed it was true. An option "start with your backup data" was presented.

The source didn't specify HOW the backup save works so I'm asking here. It is just the last previous save that was created (either manually or by autosaving) or there are some special rules put in place too? It is obvious that this undocumented feature is a fail-safe meant to be used in case of data corruption, but what are its extends?

I am not really interested in cheats, but as you may understand this seem to have a great potential for duping Pokemons, so I wonder why it doesn't seem to be widespread abused.