1.) Exposure. People don't use phone books anymore. They search Google. Having a business with no website is like working out of a building with no sign out front.
2.) Accessibility. Your website is up and running 24/7.
3.) Inexpensive. You can have a quality website for a few hundred dollars...may be less.
4.) Branding. Having your our dot comm is one of the best ways to brand yourself for potential clients.
5.) Networking. Connect your website to Facebook and Twitter and build a loyal following of customers.
6.) Convenience. Keep the world updated with the latest news concerning your business or project.
7.) Revenue. Doing business online has never been safer. Use your website as a store front for your products or to generate ad revenue.