I think dress impacts employees in many ways. There is generally a reason for most of the dress codes.

If you take a group of boys and dress them in jeans and t-shirts, then take them and put them in Suits the boys act differently. The same applies to adults but mayhaps not quite as visibly. I think if there is a "price" to the dress down days, it helps retain some of the semblance of what the people are supposed to be acting like.