Return on Investment (ROI)
With every marketing material you create, you should always define exactly what goal(s)/outcome(s) you expect to get from that project. Identifying these expectations before starting the project allows you to better target your audience and track the success of your investment.
Website goals vary for every industry type and company. One company may wish to have a website solely for providing documentation for the products they offer. Another may want to showcase their previous work for potential new clients. A third may be looking to providing marketing information on a product they sell.
The desired goals should be written down and referred to throughout the entire life of the project to ensure that you remain on track of the importance of your website.
One way to come up with additional goals for your website is by looking at well done websites by other people in the same industry. This is also a good way to get ideas on how to structure your website.