Its for the photos, in a nutshell the 'chat' will inherit/show you albums from everywhere that the user/group is a subset. For example, if you have a family group with a bunch of family photos, and you open the 'chat' with a sibling, you'll also see the family photos since the sibling is a subset of the family, unless you toggle inherited off, in that case it'll only show you albums with you and your sibling exclusively. Just a filtering mechanism for convenience