Better sound insulation can help reduce the noise level from external sources inside a home, but 1) does nothing for outdoor areas of your home (a patio or porch for example), and 2) becomes completely ineffectual if you open a window.
Indeed. For example, dual-paned windows are fantastic, but since air conditioning is relatively rare in dwellings in the Bay Area, you effectively can't use them for sound insulation for several months of the year.
