Domain names are required to locate and identify your web site on the internet.
It is essential to get the right name for your business as this not only identifies your business by name, but also helps people using the search engines to find your business by 'type'.
Lets say, for instance, your business sells cleaning products and your business name is xyz-services - it would be much wiser to have the domain name xyz-cleaning-products.com than xyz-services.com (which most people tend to do). This not only helps people searching for your type of product but also give better placement in the search engines (read more about this here). Another good example of this is B&Q - their domain name is D.I.Y.com