Site overlay allows you to monitor click-through rates on your blog.
This is particularly useful for monitoring progress of a particular part of your blog or to track banner campaigns within a given date range.
Google does this by placing an overlay of mini indicators next to clickable links on your webpage.
Stats from this tool can prove useful for a blogger in determining which area of the blog is performing well.
Generally, the first fold of your webpage gets the most level of activity. This is the part that is viewed immediately before the reader scrolls down to view the rest.
Depending on your setup, by default, site overlay would only track internal links and not external.
Not only does it display number of clicks on a particular link, it can display revenue or profit associated with each link or page
Pingback: Tweets that mention Site Overlay from Google Analytics | Your Blog Tools -- Topsy.com