I run a breather filter.

It is mainly for bling, but it does have a function. When the PCV valve sees anything more than vacuum, it will shut and crankcase gases will back up into the system causing poor ring seal and blowby. The filter just allows air to flow both ways through the system in case you are in boost and the crankcase is pressurized.

Another reason I have it is because when I connect that hose to the intake piping, the compressor sucks oil vapor from the valvetrain into the turbo and intercooler piping. So it keeps everything clean down there.