When you click on the Comments button, a left-hand pane opens where you can chat with other Users. Each Workbook's Views have their proper comments. Any User (who is allowed to do so) can add a comment, mention other users, and add a snapshot of the current View. 

Comments are a great way for you to add more information about your Views. Other users can also use this feature if they spot mistakes or if they have questions. 

As you saw, publishing a Workbook isn't just about making it safe and visible for other users. Some features, such as Alerts or Subscribe, open completely new ways of working with your data. Let's see another way of interacting with Tableau Server Contents with Web Authoring.