I also agree. That scene shed light on several issues. It showed us why Hagen became consigliere; detailed the tensions between Michael and Vito; and also showed that Vito disapproved of Kay. At the beginning of that deleted scene, Vito says to Michael: "Did your American girlfriend get home ok?" If you look closely, you can see him roll his eyes--a brilliant little piece of work by Brando that reinforces his disapproval.