Having a web site means that your business has an online identity. While that alone does not say much, consider the following gains:
• You can target information at those searching for your particular products and services.
• Information is available to all customers, both current and potential future clients.
• Reduced costs of providing promotional, technical and corporate information. And, less printing costs, as visitors can print it themselves
• Advantages in consumer marketplace. You will have more exposure to targeted Internet users when compared to your competitors without sites.
• Unlock potential to grow business and reach new local, national and global markets.
• More effective and affordable use of marketing budgets.
• Extremely flexibile. Add, remove or change information instantly.
• Obtain information from your site's logs... Where they come from, how they got there, what they were searching for, etc.
...Just a short list to help you in pursuading the others! :)