i'd imagine they may help keep your engine bay temps down but only minimally.. since there are lots of other hot bits in the bay anyway..
i'd advise against it.. since it may overheat the turbo if running hard for extended periods.. i'd like to think if i'm in constant motion (like on the freeway), the turbo is sufficiently cooled as the vehicle travels forward..
It will keep the heat from the turbine housing away from the compressor housing which can help to maintain a consistant intake temp when using the car for competition. Would also work on a road going car especially when driving the car hard with hot weather.