Google Analytics is a reporting tool that allows you to track your website visitors and their behavior on your site. You can use a different software to track this information, but it's important that you track it somehow. If you manage a large site with significant web traffic and more detailed ecommerce capabilities, you might want to look into an enterprise software like IBM Digital Analytics (formerly Coremetrics) or Adobe's SiteCatalyst. For small business website data analysis, I like Google Analytics. It's easy to use and free if have an account with Google.