Say I am working on a rails project. I need vim open with root; I need rails server, console, dbconsole; I need one window at project root for misc task; and I prefer not to navigate with the mouse to different tabs. Personally, I vastly prefer tmux terminal multiplexing over terminal tabs.

Also, it doesn't happen frequently, but I have closed terminals which I didn't mean to. tmux/screen means that causes only minor inconvenience, compared to closing the terminal, opening it again, opening all tabs, dealing with swap files, re-running servers, dbconsoles etc.