Read only from what I understand can download a preview and any renditions and that is it. But it is allowing all user to upload the asset.
Read/Write can delete photos, can create subfolders, and ???? but can't ????
Read only = only download renditions (only you specifically grant access tothe originals)Read/write = download all versions, create sub folders, delete assets,upload assets and edit metadataFull access = same as read/write plus edit folder settings