obviously, suburbs use up lots of land so there is loss of agricultural land and open space...here in Central FL where citrus used to be king, we can see where the next phase of sprawl will occur by looking at the condition of still-existing groves (FL's citrus industry is marked by its own disgusting history, but that's another story)...and where planned residential development may leave up to 50% of the land as undeveloped open space, typical sprawl uses up nearly all open space... so there is a loss of both agricultural land and open space...
in addition, the growth of US suburbs may be understated by the fact that cities have succeed in annexing many residents in a number of sprawling metropolitan areas of the Sunbelt...for example, Oklahoma City (not exactly the first metropolitan area one thinks of) encompasses more than 600 square miles...
and some people have opted to move away from the immediate metro area entirely, and are living in small towns (for the time being, anyway) within commuting distance...according to urban geographer John Friedman, 90% of the US population lives within a 2 hour auto drive (a not entirely uncommon commute) of a core area of 300,000+ Michael Hoover