Anything printed starts with an image of some kind. Even a word is an image in the printing process. And when you are using four color printing, the image is EVEN MORE important. Quality is one issue. Style is another.
Experience is important too.
A professional has done it before. No need to waste time reinventing the wheel, and in your business, time really is money. Availability is another consideration. Your cousin Jack with his Canon might be in Mexico on vacation just when you need that postcard shot done. Rates for professional photographers are very similar in all parts of the country.