I looked into this just a few weeks ago. Something to maybe try in the future but no big hurry. It's big on Motorcycles, likely do to the long stroke of V-Twins and low RPM.
The device is a type of check valve that allows pressure to escape, but will hold a vacuum. As the cylinders move up and down in the crankcase, they alternately create vacuum and pressure. What this device does is pass pressure, and hold vacuum. Like a vacuum pump, the idea is this holds a vacuum in the crankcase to improve horsepower as the crank/rods/pistons then don't need to loose energy moving through air. Oil mist will also drop out into the oil since if there is a vacuum, there isn't any air there for the mist to stay contained in.
It also works to keep pressure out of the crankcase. Not a problem on our cars as our blower outlet doesn't have any fittings attached to the crankcase. A retrofit turbo that is ahead of the Throttle body would.