Tightening up a house to an arbitrary and capricious value established just for the purpose of avoiding having to install a ventilation system and avoiding having to meet the combustion safety provisions of the building code, but making it look technically sound because a geek with a blower door did a test.
The group that really has me confused are the PassivHaus folks who are pushing 0.
Under some , , , , , and standards, structures must be more air-tight than other lesser standards.