A bit of real world experience:
When I replaced the hood on my 71 C20 truck (rust issues), I decided to use a cowl induction hood instead of a plain one. One Saturday I spent all day washing, polishing, waxing and buffing the truck...looked great (but I digress)....
The next morning I went for a drive on the freeway. There was a bunch of water droplets all over the truck (overnight dew). As I drove, I noticed that the water from the hood, and the windshield cowl was actually getting 'sucked' into the opening of the cowl induction of the hood. This began happening at about 35-40mph, and became more vigorous as speeds increased (got up to 80MPH before backing out). That made me a believer.
Tim