Nail polish gives your hands a finished look. And manicures in general add class to what otherwise may be your average looking hands and nails.
I would never go out without my nails polished. They elevate my outfit, convey a sense of style, and display my sense of aesthetics and femininity.
One of the first things people look at (so they say) after my face and outfit are my nails.
Source: http://myfolio.com/art/08nz1c4bsy