Groups > Will allow specific members of a group to be able to see specific folders that are hidden from public.
Protected Folders > Add a specific folder to a specific group that allows members of that group to view or optionally add photos as well. Options to allow adding photos to a folder would be decided by creator of the folder.
Example: I will want to create a travel "Country A" folder for Friends "A" group - to see my trips and possible add more photos to specific folders
I will also want to create another folder " Country B" folder for friends "A" group
I will then also want to create a "Family Photo Album" for a new group of friends. Again same options to view only or view and add photos.