It is important that your site looks professional and the design is appealing. More important is that your site functions and has purpose. When someone visits your website youwant that visitor to do something. Buy something, call for an estimate, subscribe to your blog or create an account for updates. Some sites even have primary and secondary goals.
Even if your visitor does not complete the primary goal (for example buy now or request an estimate), you want them to complete a secondary goal (for example subscribe to your updates, or become a part of your mailing list) before they leave your site. When designing a site for a client we make sure that certain goals are addressed and a call to action is in place to convert those goals. Even if it is just to capture an email address or encourage a repeat visit for further information. You dont want to waste visitors, not even one.