[Neutron]

Originally Posted by Y2Kvert4me

The PCV system is setup so that the intake manifold vacuum draws the crankcase vapors out of the engine. These vapors contain very minute traces of oil, which over time, collect and form puddles of oil in the intake manifold.
The oil that gets burned also helps to carbon up the pistons over time. In short, you need to let the crankcase breathe, but you want to burn as little oil as possible, and also keep it out of the manifold.

A catch can filters out these oil mist particles exiting the engine, and condenses them into a storage can before entering the intake manifold.

Thanks for he info, I never knew..