It uses the same kernel (it's just a container) and the benefit is for example AUR without using unstable distro.
You use AUR and if something breaks, it only breaks the container.
Also keeps your base system clean if you uninstall (big reason why docker is so popular on servers). Can create custom environments for a project then just delete everything when you’re done.
Also very useful on immutable distros like Fedora Silverblue (all my command line programs and some gui programs are in a distrobox container, exported to the host so they are just there like normal).
The Distrobox assemble command allows you to install programs from a file and automatically export (unfortunately there’s some bugs I hope are fixed soon). So things can be declarative like nixos.