1. If Barbara had performed this gorgeous number at her full force vocally, she would not have been able to convey as much sifting out of the thoughts of her heart. It would have lacked the subtle attraction and vulnerability she feels about her attraction to the character of Nick. She obviously struggled with insecurities and inexperience, which is revealed not only by the dialogue, but her actions as she performs the song...we gain a gorgeous glimpse into her introspection, as a woman, not as a performer, through her interpretation and action, portraying Fanny.
2. She is nervously flirting, rather coy and shy...he is giving her enough space to sing out her heart and explore her feelings, as he is standing a bit apart, merely watching. There is a distance he allows her, of safety in that space. It also seems that she is fearful of even admitting her attraction to herself, much less to him, in her quiet whisper of the lyric, "a very special person." There is so much brilliance in this scene, by all involved both in front of and behind the camera, especially Barbara.
3. Showing her walking away and the use of arm movements and space support Streisand's performance. The use of a storefront, a gathering place for people, in the barber, was also a lovely touch in dealing with community, the walking out onto the street from the alley, also depicted that beautifully...that people truly do need people. There is also the gentle smile, as he is listening, through the direction of Nick's reactions and the way that the camera shows them both in the scene, so that you may see those reactions is brilliant. It would not have meant as much if she was the only person in the scene...the lyrics are highlighted by giving the audience a glimpse of more than one person...the humanity and direction beautifully intertwine.