Flexibility, extensible, lot of community working around it so you have information on how to do anything. Being a terminal editor, you can use it everywhere, and since all the configuration can be backed up in a file, you can use it everywhere with your own settings.

It is very useful when doing native coding like in C/C++. This is also very useful in writing shell scripting. You can customize the configuration of vim editor and create your own shortcuts for editing.

Oh man. I love vim - it's the One True Text Editor. The keybindings and commands make working on software so much easier and faster. I really love extending it and writing code for it as well. It makes for a fun project, and is very customizable.