The technical term for air exchange rate is Building Airflow Standard (BAS).  The BAS is determined by the volume of the house and number of occupants.  If a blower door  test shows that the air flow in a house is above the BAS, then the house is excessively leaky, loosing conditioned air to the outdoors and wasting money.  If the house is below the below the BAS, it might need some mechanical ventilation added to remove possible stagnate air, moisture, or indoor air pollution.  Extreme cases of low air changes could cause mold and structure damage.  Air sealing should be done in conjunction with a blower door, so that air flow can be reduced to a specific level.  The most accurate control of a home’s heated space is accomplished by sealing as many leaks as possible, bringing the air exchange rate below the BAS, then introducing makeup air by mechanical ventilation.  Even though optimum performance is achieved by reducing air flow below the BAS, most people opt to achieve great energy savings by reducing the air exchange rate just down to the BAS, while avoiding the expense of adding mechanical ventilation.