It’s almost impossible to over-stress importance of using a good web analytics software. Launching a marketing campaign, making changes to a website, really making any marketing decisions at all without first finding analytics data that backs it up, is just taking shots in the dark.
Web Analytics as a way to justify marketing decisions
Operating without analytics [...]

Conversion Optimization is  using technology to test variations in page design and messaging in  an effort to maximize the conversion ratio, or the number of website  visitors who become paying customers; particularly important for e-commerce  sites and sites with higher traffic-levels.