Members of the site each have a user profile and can upload research output including papers, data, chapters, negative results, patents, research proposals, methods, presentations, and software source code. Users may also follow the activities of other users and engage in discussions with them.
Here is the official word from Microsoft TechNet, The C:\Users folder is shared when any sub folders from C:\Users\<username>\ is shared. The article is stale and mostly unhelpful, but worth knowing to complete the story.
4. Check to see if a folder is shared. To view the sharing details of a folder or file, open Windows Explorer by clicking on the Start button or Windows logo on the bottom-left corner of your screen. Click on your user name to display your folders and files.