I have to disagree with what some people have posted.
Think about it this way. Before you have ever opened your mouth to say hello or smiled, people have already made a decision about you based on what you dress. If you look sloppy and gross, people may think you are lazy and don't care. But, if you are well put together, people may think you are competent and know what you are doing. This may not be true, but first impressions can actually stick with someone for awhile. This is especially true if you are going somewhere for a job interview.
Just my opinion though. No one can force you to wear anything you don't want to.