I remember reading (years ago, when I was newly Catholic) the Catechism's section on modesty. "Modesty protects the intimate center of the person," it said. What a perfect summary, and how much sense that made to me (and still does.)
Further, I remember a priest talking about modesty being charitable and loving. It is a kindness for men and women to dress modestly for one another, because modesty shows a respect for the dignity and humanity of the other, and seeks to avoid arousing a purely physical response.
Here is a wonderful article by Dr. Ted Sri of Benedictine College about modesty, and here are the references in the Catechism of the Catholic Church, under the heading "The Battle for Purity." (See especially paragraphs 2521-2527.)