A very important part of business is balancing the numbers. When selling products or services online, it is vital to have sales statistics in some form.
Google Analytics allows you to track many areas of your Google Site. Like Visits, Bounce rates, General SEO , Goals and eCommerce Goals of your website.
Google Checkout Information that is tracked by Google Analytics here :
Setup and Tracking Goals
Funnel Goal pages like 'Thank you' and 'Cancellation'
Setup and Tracking eCommerce Values