It was more of an issue with carburetors. At near-freezing temperatures the carburetor venturii would cause a pressure drop that allowed atmospheric water droplets to condensate and freeze on the carburetor jets. You'd fire your engine up, get a mile from home, and if you were aggressive on the throttle, you'd freeze your carb and be stuck in the cold a mile from home. Since exhaust manifolds heat up quickly, they put cheesy metal hoses from the exhaust manifolds up to the air filter housing. It worked decently on carbs, but since EFI doesn't require a venturi, there's no need any more. In summer months they also duct hot air up to the intake tract, so southern guys like me always removed them.
