Short answer -- yes. If you are in business for yourself, a website is the most essential, and most cost effective, marketing you will ever do.
Most young people now use their smart phone to look for service providers. Those big old bulky phone books are rapidly disappearing. If you want young clients / patients to find you, you have to be on the internet.
It's becoming almost a reflex these days to hear about a business and go look at their website. Even baby boomers are turning to online directories, and review sites like Angie's List and Yelp to hunt for services and see what others have to say about them.
If you aren't on the internet, you are risking your business security. It's just that basic.