Why do I need a website?

Rather than thinking about needing a website, what every small business should be thinking about is a sales funnel, which is clear system that leads potential buyers through your marketing, educates them about your product or service, builds a relationship with them and gives them a reason to do business with you

A website is a really effective way of achieving this, but too many businesses focus on getting the website and not on what it's actually supposed to be doing

This article goes into more detail, and gives you some ideas as to how you can implement this concept in your own small business: UpBound Blog - Web Designer Confession: You Don’t Need A Website.