Depends on your biz. A website is never a bad idea. That being said, I know a couple law firms that get all their business from referrals and are happy with the size of their firm / not looking to grow.

Personally, I feel it is a big red flag when I am looking to work with a business and find out they don't have a website. To a certain level it detracts from their legitimacy.. Kind of like not having business cards or super cheap ones from Vista Print.