The "correct" answer really depends on your driving environment. I personally saw the intake tract of Duramax engine pickups (stock and K&N) that ran the GM air filter test in Arizona. Huge difference in how much superfine matl gets in there.
OTOH I knew a guy who ran a 283 Chevy in Cleveland Oh for 100,000 miles with NO air cleaner at all, and it ran fine. That's an environment with a lot of rain/snow, little dust, and he ran 100% on paved roads.
OTOH I knew a guy who ran a 283 Chevy in Cleveland Oh for 100,000 miles with NO air cleaner at all, and it ran fine. That's an environment with a lot of rain/snow, little dust, and he ran 100% on paved roads.