Ssh – the bind address used for when forwarding a port via SSH

I have a brief understanding of port forwarding via SSH. So let's say I have a VNC server up and running at port 5901. I pick up my laptop, go to work, then I want to connect to my server, but I want an encrypted connection, so I tunnel everything into an SSH connection as follows:

ssh -L 666:localhost:5901 user@home_ssh_server_address

I tell my VNC client to connect to localhost:666, and I'm good to go.

Now, reading through the SSH man page, I found that I can specify a so called bind address:

ssh -L [bind_address]:666:localhost:5901 user@home_ssh_server_address

Thats where my question comes in:

What is that bind address good for?

Any help is appreciated.