The Vulcan Science Directorate has determined that it is a remnant from the time when the foot was used to grab things and the digits of the foot were bigger, where it served as structural support for the tip of the toes.
@ragingloli
You mean that you never pick things up with your feet?
The function of your little toe is to help you maintain your balance. The function of its toenail is to offer the appendage some grade protection from a rough world.