It is a nice feature, though secure folder does the same job, just with a ton more security.
If samsung added app lock, people might use that instead of secure folder. This would unintentionally reduce security for everyone who didn't realise secure folder exists.
You can set an app up in secure folder, set secure folder to lock maybe when an app is closed. Hold your finger on the app, press send to home. Now you have a secure folder locked app that shows on your normal phone. Press it, authenticate, app opens. Only downside is you need to enter your full code once each phone reboot but that's not too hard
