stuffing that filter on your PCV.... is kinda pointless...

some people do it cuz it looks pretty... well, most people do it.

and there are a few hardcore ones out there that do it because they want to keep their throttle body clean...

there's other alternatives if you want to keep the stuff outta your throttle body... ie: greddy's oil catch can...

and er... with those things on, usually u can't pass the visual inspection part of smog test... since the stuff that comes outta the PCV (positive crank ventilation) valve is bad for the enviornment...

thats why manufactures get a hose to connect it to the intake airbox and suck it back in the throttle body...