Pro Ubiquity and portability
Vi/vim exists on almost all Unix-like platforms, it is the de-facto Unix editor, and is easily installed on Windows. All you need to make it work is a text-based connection, so it works well for remote machines with slow connections, or when you're too lazy to set up a VNC/Remote Desktop connection.
Pro Keyboard-based, mouse-free interface
There's no need to reach for the mouse or the ctrl/alt buttons again. Everything is 1 or 2 key presses away with almost 200 functions specifically for text editing. Vim does support the mouse, but it's designed so you don't have to for more efficient usage.
Versions of vim like gVim or MacVim still allow you to use the mouse and familiar platform shortcuts. That can help ease the learning curve and you'll probably find you won't want to, or need to, use the mouse after a while.