A properly working PCV system should allow a small amount of vacuum to the crankcase, so that it pulls in just a very small amount of fresh air through the breather tube.
My car had more blowby than the PCV system could handle. Instead of fresh air being drawn in through the breather tube, oily blowby gasses were being pushed out, which would make the air filter all oily and dirty very quickly, and sometimes there would be puddles of oil in the air cleaner. This seems to be a common problem on a lot of 258s.
My solution puts the crankcase under constant vacuum. I closed off the breather hose by putting the check valve in, so no fresh air enters the crankcase anymore. If the line were left open, it would cause a large vacuum leak.
Jeep 4.0s used a system called CCV, where they used a metering orifice in a a vacuum elbow to put vacuum on the crankcase, however, the CCV system, has a breather hose that is always open to the atmosphere.
In the end, all 3 do the same thing, just differently. They are all used to pull blowby vapors from the crankcase.