Not in the US. It is segregating cities between places people work at, places people shop at, places people live in buildings with multiple units and places where people live in single family housing, without any intermingling. Trying to build a triplex where the neighborhood might already be zoned for it, but where most of the buildings are (or seem to be) detached houses is also an uphill battle because neighbors will fight tooth and nail against "changes to the neighborhood character". This leads to the only multi family housing that has gotten built in recent history to be larger towers, which leads to what urbanists call "missing middle".