Your home should have a complete thermal boundary starting at the basement going up your walls and ending in the attic.  A nice thick coat keeping in the warmth in during the winter and the heat out during the summer.  If the insulation in your home is incomplete or the air sealing is missing in places then you are paying for heat to leave your home during the winter and over paying trying to keep the heat out during the summer.  Why throw that money away.  There are great rebates offered by Mass Save to help offset the costs of weatherization home improvements.