One of the "unintended consequences" of mandating closed vent systems such as PCV was a dramatic increase in engine life between overhauls. One of the main byproducts of combustion is CO2, which is a good thing until some of it makes its way to the crankcase via blowby on a somewhat worn engine. CO2 + water vapor = carbonic acid (Coca Cola). Unless there's some sort of constant ventilation of the crankcase, the acids and other contaminants formed by combustion byproducts have a habit of eating engines for lunch. Filtered air pulled into the engine after it goes through the carburetor air filter also reduces abrasive wear from dust and other contaminants that road draft systems can allow to enter the crankcase.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!