Prior to the current Family Tree structure at FamilySearch, it worked more like Ancestry where users had individual trees. They attached sources to those trees. Those sources were migrated into the new tree. If you can find the profile on FamilySearch, some of these have enough in the way of citation information to be useful, most do not. Most of these profiles have more detailed sources attached at this point, but a link to the FS profile in the "See also" section of the sources is probably sufficient for anyone wanting to explore these old "sources."