when I’m virtually on the street where you live

All About Eve (1950) contains a brief scene of Eve Harrington (Anne Baxter) and Addison DeWitt (George Sanders) walking along a back-projected street, something I’ve rarely seen. I wonder why it was done. — Ah, on second thought: The street appears to be a real one in Connecticut, and back-projection was easier than taking the actors there (from Hollywood) for one shot.