linux – Can somebody explain the -R option for userdel command?

Some userdel versions have this option:

 -R, --root CHROOT_DIR
     Apply changes in the CHROOT_DIR directory and use the
     configuration files from the CHROOT_DIR directory.

In other words, instead of editing /etc/passwd and friends,
you’re editing CHROOT_DIR/etc/passwd.

For example, you might boot a live CD, mount the hard drive as /mnt,
and then use -R /mnt to edit its users.