Two terminal windows open, one with a bunch of long running watch tasks, the other with an editor. Each of the terminals is a view into one of two windows in a tmux session. Useful for having a vertically split screen with editor on right, and switching between a browser and other command windows on the left.
In first terminal:
tmux new-session -s first
tmux rename-window editor
emacs
or whatever
In second terminal:
tmux new-session -t first -s second