Depends on what you're building a website for. For example if you're a business then having a website is a must. 79% of potential customer's check out/google a business on-the-web before actually making the trip to the store.
Having a website is one of the best ways to be in front of your potential customers.
Companies spend millions creating brochures and distributing them. By having a website you can skip that entirely. Your potential customers can find out about you and any of your products online. If you get most of your business through networking and personal connections, then they will want to check out your website.