The purpose of a website varies by the type of business you have and what you want the website to do. For the most part, a website will act as the hub for your online marketing, a brochure, a store, a modern phonebook, and a tool to convert visitors into customers. The choice is yours!
The biggest point is that your site must work with your overall marketing plan. Everything you do outside of your website should be reflected in your site, that is, the marketing tone and your aesthetic.
A website beyond all the shiny bits, is really a marketing tool.