Traditional materials still have a place though. Material science has not beaten down feathers or wool yet, for the most part.
It's a way to shed water: Wearing waterproof, non-breathable layers often is worse than not, because the moisture your body releases and that gets trapped soaks you from the inside as surely and rapidly as the rain. (Maybe it's a bit warmer.)
While dry, or intermittently wettened (so it can still shed water). Numerous independent tests show that it doesn't breathe at all, once the surface is fully wet. Also, Gore-Tex is no longer best-in-class amongst rain-shedding breathable fabrics; it simply has name recognition.
To be fair, few things do breathe once their surface wets... but wool's surface is so convoluted by the twisty, hydrophobic threads that it rarely gets fully wet on the surface.