Airtight homes need some sort of system to provide fresh air and to exhaust indoor stale air.
If you are living in a very airtight home, in a harsh climate - where opening the windows for fresh air involves a significant energy penalty - you need more than just a simple bathroom and kitchen exhaust fans.
Obviously, if you live in a climate with mild temperatures on most days, during a large part of the year, you may not need mechanical ventilation - at least during the periods where it is possible to rely on natural ventilation, that is, during the periods where you can open the windows or vents to get fresh air.
Just keep in mind that air infiltration through air leaks or through openings such as chimneys and fireplaces isn't a true alternative to bring fresh air into the living space.
Air infiltration is a source of over-ventilation or under-ventilation, higher energy bills, unhealthy air quality and moisture damage in the home's structures.