Usability Goals: Utility of a Website Design
Does a website do what it should do? Does a website offer the tools visitors will expect to find when they visit? Utility is a measure a website's functionality. When we design a website, we take steps necessary to determine what users will expect to find and what tools they will need to complete tasks. Then we give it to them.
Every time a visitor can't do what they need to do on your website - they will leave your website and find another source. The more times they have to leave, the less likely they are to come back. And, there is no bigger drop-off in visitor loyalty then the first time they have to click away from your site.
Don't give your visitors any reasons to click away from your site. Make sure it offers the functionality they require.