How did your visitors find your Web site? Did they arrive through a Google, MSN or Yahoo! search? What keywords did they use to find you? How are they using the site? Are they downloading your free content but avoiding the for-sale items completely? Are they frequenting one page more than others? Where in the world (literally) are they located?
Imagine how having this information could help you target your audience. You could use the information to design more effective marketing campaigns, increase click through rates to other pages or advertisements or to optimize your site for better search engine results so people on the Web can find your site.
Google Analytics can help with all of the above. It is a free tool from Google that will help you tune your site for search engine optimization and to better meet the needs of your audience.