1 By making an account you get closer to your audience. You will get both good comments and bad comments which, if given enough care, can help you upgrade your image and your services
2 Visibility. Let's say you have 10 followers and out of them 2 relay your informations. Your followers followers will then recieve your information and some of them will like your informations and pass it along... with just 10 followers you can reach the whole world if you have just 1 brilliant idea!
3 Advertising. Even if you have no followers, if you simply make a banner or a small movie, you can make an add on Facebook. For 10$ a day you can reach up to 1000 peoples and thanks to the informations your potential clients leak by themselves on Facebook, Facebook will identify and serve your adds ONLY to peoples that may be interested (you can chose to send the message to only women between 30 and 40 years old working in farms in the hongkong area and facebook will search them for you!).
4 Clients DATA. You will know who like your products, where, why, when they like it and may be able to deduce the future sales, best times to introduce a new product and eventual sh*t storms.