Some of the best neighborhoods I've seen/lived in in America have been neighborhoods that were built ~100 years ago when zoning didn't really restrict things. You'd end up with mansions next to smaller homes next to duplexes and apartments. Some of the mansions end up divided into multi-unit housing. A person can be born in the neighborhood, and live their whole life there moving into different housing types as they need to. You can end up with greater social cohesion across age and socioeconomic ranges. If a kid from a working class family grows up in an apartment across the street from a wealthy kid, they will have more social mobility than of they were in segregated neighborhoods.