Google My Business, Yelp, the Yell.com etc. are all online directories that contain thousands of Local Listings. Those Local Listings include a business’s NAP, and other details about the business, such as its hours of operation. They have largely displaced their printed predecessors and many have kept their name (e.g. Yellow Pages).
This is a common question, especially with businesses that know most of their customers. Businesses whose customers are mostly within ten miles often believe that online promotion is a waste of time. Even the smallest businesses that know their customers personally can benefit from Local SEO if they would benefit from new customers.
Some businesses eligible for a Google My Business listing may choose not to have one and if they do that then they will lose out on a lot of potential business. That is because without one they cannot show up in the “3-pack” search results. This is true even if they have the best website in the world.