In one of my groups it came up that we would like a set of files to be viewable/editable by any member, and a select of core documents to only be viewable by the members, but moderators/owner can change the contents.
You can do that in the group's Wiki. When you create or edit a page there's an
Only moderators can edit this page checkbox.
At present the Wiki lacks some of the structure of the Files section (like a sortable list view of all the pages), which can make it awkward for some purposes. On the other hand its text content doesn't count against your group's storage (but photos or other images in it do).