If I take a picture on my phone, it syncs to my laptop and desktop. If I put something on my computer in my OneDrive folder photo folder, it shows up in the photos on my phone.
You share a folder, update a file and then the other person does not get the update to that file, so then they are sitting there on the phone with you saying "no I don't see the updated file" and you have to have them login to the web version and basically download the file to their one drive. That happened to me several times and I just gave up on One Drive. I don't know if they fixed that. Yes, it syncs things for YOUR folders but it will not sync things to shared folders.