Web analytics provides information on a site's performance based on the results from statistics gathered gauging many factors including site's performance and usability. The data and statistics need to be analyzed by someone who can judge a site's worth and functionality based upon these statistics. An understanding of the retrieved web analytics can help optimize SEO usage.
Many sites and businesses looking for SEO help may be able to perform some of the other tasks themselves but often times the analysis for the web analytics will be handed off to SEO companies and professionals. This is because the information is so important and an error in the analysis can alter SEO techniques and even an entire campaign. Proper understanding of web analytics can allow a site to see which SEO techniques are working and which may not be.