It's been a few years that Samsung phones ship with the company's Knox technology. Secure Folder leverages this offering to create a local sandbox that's encrypted and separate from the phone's standard apps. Although this may seem like a niche solution, the app has now been downloaded more than a billion time on the Play Store, confirming its popularity.
If you're unfamiliar with Secure Folder, it lets you store files separately, isolate apps from the regular ones, and add an additional security layer with PIN or password protection. The app is particularly useful if you use a single phone for your both work and personal matters, as it lets you use them separately from each other, as if they were installed on two separate devices.