https://fs.web.illinois.edu/Insider/2022/06/16/consider-the-envelope/ 

"Indoor air quality is important for the health and comfort of occupants. Indoor airtightness can help provide good indoor air quality by making it easier to control the indoor environment with ventilation. Additionally, airtightness is key for energy efficiency. It is not uncommon for discrepancies between expected energy usage and actual energy usage to be explained by air leakage, and so making buildings tight is vital to meet energy and climate goals."