while i was in a group interview at SPJIMR, one of my fellow interviewee asked the panel informally "why is it so necessary for people to turn up in suits for interview?" The lady in the panel said this:
"Imagine you are sitting in a hospital waiting to meet a specialist for your father/mother who has been having some ailment for a while. Suddenly, a lady walks in wearing a micro skirt, stilettos etc. She walks up to you and says Hi, I am Dr. X and will be treating your father/mother. At such a time, what would your first reaction be?"
The guy who had asked the question replied, "I will be shocked, maybe even think she should be working as a model or something." To which the Panel lady replied, " Exactly ! You will judge her from her first look, she may not look one bit like a doctor and so you suddenly will have doubts about her ability right ? First impressions do matter and you can say a lot with the right clothing. So when a interviewee walks in a Business suit, clean shaven and overall looking smart, we know that this guy means business. He is not casual and it will be worth talking to him.
So, it is important to look smart and be comfortable at the same time.
Remember, actions always speak louder than words.