The PCV valve uses engine vacume to suck out combustion gasses that get past the rings. The line from the air cleaner to the opposite valve cleaner provides replacement air. The engineering intent is a flow of air from one valve cover down through the crank case and out the other valve cover. This movement of air draws out moisture as well as combustion gasses and helps to prevent internal rust and the formation of grease like deposits. If you do not want to run a line to your air cleaner you can buy a plug in cap like vent from just about any hot rod supplier. These caps are not as good, in my estimation, as the hose because the air intake filter does a better job than the mesh in the cap. But what do I know.