The short description field is shown to prospective customers on the search results page. Having an attractive description helps differentiate your business from its competitors and can ultimately help gain you more business by increasing the number of clicks through to your profile.
It is complusory for all businesses to fill out this field. It is highly preferable to make your short description UNIQUE(and not just pasted in from your website). Simply entering a list of keywords will result in your free listing being declined.