Looks like it executes the commands only on the server where
~/.ssh/rc or /etc/ssh/sshrc exists.
> ~/.ssh/rc
> Commands in this file are executed by ssh when the user logs in, just before the user's shell (or command) is started. See the sshd(8) manual page for more information.
I use it for updating a symlink in a known location to point to SSH_AUTH_SOCK. I then get tmux sessions set up to look in that location. Effectively, each time I ssh in, I fix all the ssh forwarding in active sessions (this is on local dev vagrant machines).
> ~/.ssh/rc
> Commands in this file are executed by ssh when the user logs in, just before the user's shell (or command) is started. See the sshd(8) manual page for more information.