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.
Share files over a home network or on a shared PC. To share files and folders on your network (homegroup, workgroup, or domain) or on a PC that you share with other people, you can also use the Share tab in File Explorer. The next sections provide more info about this type of sharing.