Wouldn't it be nice if your job didn't involve wearing something starched and confining every day?
While dress guidelines vary from company to company, some jobs trade traditional business attire in favor of a more casual sense of style, whether it's done daily or only occasionally. Other companies may favor T-shirts and jeans to collared shirts and ties.
Often, what constitutes a dress code comes down to a matter of company culture, your role at your job and how much customer interaction you have while you're there. Technology, design and manual labor jobs tend to be a little more lax, while jobs that involve face-to-face customer interaction tend to be all business.