You have to realize some people's legs may not be as nice as they would hope. They might have bruises, scars, birth marks, bad skin, saggy skin, etc. Using nude stockings covers all that up. But yeah if you have perfect legs, go bare.
Myself I find nude stockings a bit creepy and old lady like if you see a woman in just her stockings. On the other hand if all you can see is the hose as she's wearing a sexy dress over top they can look quite nice.