The importance of that type of redundancy depends on the viewing habits of a particular person. In the case of my friend, the "don’t actually use our DVDs all that often" really was "never re-watched the DVDs she owned". She had a DVD collection with all the X-Files seasons, James Bond movies, etc.
But she inadvertently learned her true viewing habits when Amazon Prime included video streaming for free. She realized she always preferred watching something new on Amazon rather than play an old X-Files DVD.
But what if Netflix and Amazon Prime Video lets their streaming licenses expire for "X-Files" and it's no longer available? Wouldn't that make the X-Files DVDs a great backup?!? It would, if she actually re-watched the X-Files -- but she never did. Owning DVDs was a waste of money for her particular viewing preferences (new stuff instead of reruns) and she was happy to get rid of the clutter.