- A single file for many different icons.
- Many possible variations: size, color, shades, rotation, etc.
- Display equally great on all screen sizes and resolutions: PC, TV screen, Retina, etc.
As an aside, you need a solid IDE (and a good knowledge of it) in order to quickly locate the needed file with a grep-like tool.
You also need to get acquainted with pre-compilation tools, to make your life easier.