Visitors tracking means tracking down the visitors of your site . This can be a very detailed thing. For example you can also track that how the visitor came to your website.
What item he was looking for while he visited your site. Visitor tracking and analytics also include the pages your visitors entered on your site. You can also track the page
after which the visitor exited your site.
If most people are ending on checkout page after the sale then this is really a good and healthy sign, however if people are visiting the site and then leaving without purchasing any thing then it must be of concern for your . So it is a a must to install visitors tracking code to keep track of these things.