tmux really comes into its own when you combine it with Vim and FZF [2]. I was initially hesitant to try tmux, but once I themed my tmux.conf and nailed down the keybindings, it became indispensable to me. I now use tmux as a basic organizational tool, and I always have at least one tmux session running on my desktop.
I have Ctrl+A+S bound to split the tmux screen horizontally, and Ctrl+A+A to toggle maximizing the tmux pane. Shift-DownArrow opens up a new tmux window to the right of the current one. Shift-LeftArrow and Shift-RightArrow move left and right between the tmux windows. I wanted it to be reminiscent of URxvt tabs.
Another one of my favorite bindings works as follows: visually highlight a line in Vim, then hit <leader>tj, which sends the highlighted line of code to an open terminal in a split tmux window below. Very useful for REPLs. You can also open Vim in the lower split terminal and use the same keybinding to send text directly from one Vim instance to another. It uses vim-tbone [3] and some custom bindings from @junegunn.
[1] https://github.com/atweiden/dotfiles