Virtually any type of business needs a website. Whether you are a local restaurant, a one-person CPA, or a busy manufacturer, your website is the proof that your business has a pulse. Like it or not, this will be one of the main conduits your prospective customers and clients will use to find you.
Even if your website is an afterthought, you should consider auditing it and refreshing it at least every couple years. That might not mean a full redesign from the ground up, but it definitely needs to reflect your business and provide your visitors with enough information to take the next steps.