Think of it this way, if you go to the dentist for a routine check up, would you prefer to see a well groomed person in a white coat work with their hands in your mouth, or a mechanic with oil stains on his overalls? Remember, first impressions last. You need to hook your customer from the moment you hand them your professionally designed business card. The same concept is relevant in regards to your adverts, logo, website, etc.
Your customers want to get the impression you are a professional in your field.