I agree with everyone else that it's great on remote systems, but the reason I use it locally too is because I can set up all a project's "tabs" with just one command. I have dozen-line scripts for each client/project that will either create or attach to a tmux session, and when creating set up all the windows how I want: setting their names, cd'ing, opening psql, tailing a log, changing the bottom color (green for development, yellow for staging, red for production), etc. For Rails work I typically have separate windows for models, controllers, views, stylesheets, and javascripts. It makes it really easy to get started after a reboot, or just hide projects for a while and bring them back quickly.