1. Emacs isn't always on all the systems, and getting it downloaded/setup can be a pain in the butt
2. Sometimes it's just easier to launch nano quickly to edit one line in a .bashrc from the command line
3. When I bork Emacs and it doesn't work, it's nice to be able to fall back on a simple editor to edit my .emacs.d
4. It's nice to have an alternative to vi with keybindings I'm more familiar with