Train went into a tunnel halfway through a database migration. The SSH session died. Five years ago that would have been a cold sweat and a long evening untangling a half-applied schema. This time I shrugged, waited for signal, ran tmux attach, and there it was, still chugging along exactly where I left it.
That is the whole pitch for tmux, really. Your shells live on the server inside a session that does not care whether you are attached to it. The connection is just a window you happen to be looking through. Close the laptop, the window goes away, the work does not.
The two commands I actually use are trivial. tmux new -s work to start something named, and tmux attach -t work to get back to it. Everything else is a bonus: splitting panes, scrolling back, naming windows. But the core habit, the one worth building, is simply never running anything long-lived in a bare SSH shell again. Migrations, builds, rsync of something enormous, all of it goes inside a session first.
The one thing I would change about my younger self's setup is the prefix. Ctrl-b is an awkward stretch, so mine is remapped to Ctrl-a in ~/.tmux.conf:
unbind C-b
set -g prefix C-a
bind C-a send-prefix
Small thing. But you hit that key thousands of times, and a comfortable one stops you noticing tmux is there at all. Which, when a tunnel eats your connection mid-migration, is precisely the point.