Well, the script could keep running even after he would have detached from that tmux session due to losing ssh connection. And since that script would unblock all ports after 30 seconds...

(Same use case as nohup that they mentioned)

Tmux essentially creates a pseudo-shell that persists between sessions.

So you can start a process, detach the session, start something else, disconnect, come back next week, and check on it.

It does other things too. Like console tiling.