There’s a reason why Google Analytics is the most popular platform for web analytics among business owners.

Advantages
It’s free.
Easy to use.
Powerful — You can see all the different types of analytics such as users, traffic source, behavioral and acquisition all in one place with very little to no investment.
Smooth integration — It blends seamlessly with all other Google products, everything from AdWords to AdSense, etc.
Simple user interface — Novice users can access all the different analytics from any device in the world. Traffic source analytics, behavioral analytics, acquisition analytics, they’re all available with just the push of a button.
Some Drawbacks
While they have real time monitoring, Google only reports at the hour level. You’re also limited to two dimensions at a time. For example, if you wanted to look into city, country and DMA, you would have to choose two of the three.
Despite these drawbacks, Google Analytics remains one of the most popular, widely used web analytics platforms in the world. It’s especially useful if you’re an up-and-coming entrepreneur with a small-but-growing business.

Jorge Garcia, Founder and CEO of Garcia Analytics, highlights the simplest and best way to understand web analytics: with Google’s free service.

http://www.docstoc.com/video/167391411/Why-Use-Google-Analytics