Data is synced from the Chrome Web Store. View the official store page for the most current information.
This is a great dev tool to see what data is leaving a particular site on the browser. Bonus here is it monitors other Chrome extensions data as well to see if any extensions are sending any data out. I usually have it turned on and I block all of it and it makes me feel a little better about my browsing experience. I think this is a must have for any privacy focused individual.