What do you want people to be able to accomplish on your website? Are your visitors looking for specific information on how to do something? Are they going to read through each page in turn, going on only when they're done with the page they're reading? Are they just going to start at your home page and wander aimlessly around, exploring your world until they get bored and go somewhere else?
Suppose that you're creating a website that describes the company where you work. Some people visiting that website might want to know about job openings. Others might want to know where the company actually is located. Still others might have heard that your company makes technical white papers available over the Net, and they want to download the most recent version of a particular paper. Each of these goals is valid, so you should list each one.
For a shopping catalog website, you might have only a few goals: to enable your visitors to browse the items you have for sale by name or price, and to order specific items after they're done browsing.
For a personal or special-interest website, you might have only a single goal: to enable your visitors to browse and explore the information you've provided.
The goals do not have to be lofty ("this website will bring about world peace") or even make much sense to anyone except you. Still, coming up with goals for your Web documents prepares you to design, organize, and write your web pages specifically to reach these goals. Goals also help you resist the urge to obscure your content with extra information.
If you're designing web pages for someone elsefor example, if you're creating the website for your company or if you've been hired as a consultanthaving a set of goals for the site from your employer definitely is one of the most important pieces of information you should have before you create a single page. The ideas you have for the website might not be the ideas that other people have for it, and you might end up doing a lot of work that has to be thrown away.