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.
Sharing folders. When you share a folder with someone over Dropbox, that folder and all of the files in it will show up on the other person's Dropbox account, as well as in the Dropbox folder on their device(s), if they have the Dropbox program installed.