A "local remote" is a contradiction. Unless the remote is on a different disk you are just wasting space. Even then the point of remotes is for sharing, not for backup/redundancy.
What if you have a few local machines you’re using for development, and want to keep them in sync? This method allows that single central repo without having to bounce all the code through a cloud hosting service.
The remote can be a shared directory that multiple users have access to, and the working directory is private where each user only has private read + write access.
I use them ALL THE TIME. If anything, I have my 'local remote' in my Syncthing shared dir - its great for sharing code between my dev workstation(s) w/o using Github, etc.