When it comes to Content Libraries, I would consider Salesforce Files Sync to still be in its infancy. Salesforce Files Sync works great for bi-directional collaboration between users as long as the file lives outside of a Content Library. While you can easily share a file in the "Files" tab with a Content Library, doing so means that access and privileges to the file will be governed by the library. That means going forward you would have to resort to the existing Content Library wizard process to upload new versions of files shared with libraries.

My company would also love to see bi-directional synchronization involving files in Content Libraries. But, as Arnab indicated, that is not a reality yet.