Originally Posted by Eric F

Practical reasons:
- Easier application of sunscreen.
- Easier and more comfortable post-ride massages.
- Less flesh tearing when sliding across the ground
- Easier wound cleaning after sliding across the ground.
- Better adhesion of bandages.
- Improved aerodynamic efficiency.
- No gnat catching.

Non-practical reasons:
- Shows off your well-toned leg muscles (in other words...chicks dig it).
- More comfortable for your partner when snuggling in bed (in other words...chicks dig it).
- Sends a signal to serious cyclists that you are also a serious cyclist.
- Sends a signal to shirtless guys on hybrids that you want to race.