"Is there ever a reason to have more than one..." Yes. It's called a chroot jail. One often needs mknod to build chroot jails because the program or programs

"Is there ever a reason to have more than one..." Yes. It's called a chroot jail. One often needs mknod to build chroot jails because the program or programs that one intends to run in the chrooted in the jail directory require access to certain device files.