Because a website address is easier to remember than a phone number.
Considering the exponential growth of the Internet the question is not about whether you should have a website or not, the question needs to be how soon can you get a website if you don't have it?
No matter what type of business you’re in, your organization should be up-to-date with current technologies. By having a website you will be offering your customers and clients an interface they are much used to using on a day-to-day basis; this conveys to your customers and clients that you have got a progressive thinking and you adapt to technological trends with great flexibility.
A website is a great place to showcase your work. It is much easier and quicker to update information about your products and services on your website than in print material. Unlike print ads which quickly become outdated, your website can provide current information and news. By including a portfolio or image gallery, as well as testimonials about your work, you can demonstrate what makes your business unique.
As with any business, most customers have the same set of questions. By having an FAQ (Frequently Asked Questions) online, you can save yourself time and money. You can provide more information that otherwise cannot be covered on a business card or flyer. People these days find it easier to talk through websites rather than calling up or even sending e-mails. Instant feedback from your customers and clients helps you improve your products and services with greater speed
Your website works for you 24-7. Your website is available to both your regular and potential customers providing them with the convenience of reviewing your products and services when your store or office is closed. Customers can log onto your Web site and easily find the information they want - when they want it - their satisfaction increases. There’s no pressure to drive over to your place to find out about your offering.
If you already have a website but it is "home-made", having it professionally redesigned will provide your business with a professional image which will inspire even greater confidence.