How important is dress code in school?

I am just frustrated at the high school where I work. We have a dress code, but does it really make sense? For one thing, it is selectively enforced, but that is another can of worms. But really, who can say how low is too low, how short is too short, and how tight is too tight. Does it matter? Should the school take on this responsibility? Isn’t this the parents’ responsibility?