Rob Reiner has a significant influence on this film as Nora Ephron used interviews with him after his divorce in order to create the character of Harry. It was his journey from being married into living a single life once more that inspired the character on the page. Reiner, also a producer on the film allowed Billy Crystal to infuse more into the script that would make it funnier. Thus Reiner's ability to collaborate allowed the film to become more than just his ideas upon the screen.
As for the imagery in the film, Reiner utilizes the landscapes and architecture of Chicago and New York to tell this journey story over the course of the 10 years it takes place. We watch as Harry and Sally meet in various places throughout New York City and you get the impression that they truly exist in this environment rather than simply being placed in a scenic backdrop. From their walk through the park, to their museum visit where they stand between ancient ruins and sculptures to a Giants game we see how these two people live their everyday lives. And this allows the audience to be part of every step along the journey and has us participating and feeling for the characters along the way.
So, by the end of the film when Harry finally tells Sally he loves her we exhale knowing that this was meant to be and Harry just wasn't seeing it the entire time. Reiner's influence also goes to the tone of the film. He is able to take the reality of life and make it funny. This comes from years of working in comedy, understanding rhythm and life in a very studied and detailed way. It is the intricacy of life the is revealed on-screen and that comes from craft and having lived life--both of which Reiner and writer Ephron did.
