Gaz nailed it....
Mike nailed it too. There's no harm in using one (if it's chosen correctly and it's functional) and if you live in a Communist state where they check stuff like that, then you have no choice.
Otherwise, over the years I have seen bad PCV's that have caused
oil usage and have struggled with finding correctly size valves for engines that have never existed in OEM form.
Back in the day, there were no vents, PCV valves, etc. Engines had road draft tubes and they vented pressure by dumping
oil on the road. When the government decided that had to change, auto manufacturers began to come up with ways of dealing with the crankcase pressure. The PCV valve was the most emission-friendly as it put any vapor right back into the engine to be recirculated.
It's a lot simpler to just run 2-3 valve cover/intake breathers to make sure the engine can vent and it will not cause a problem down the road since there are no valves to fail. If a valve does fail (or is incorrectly chosen), it will allow the engine to pull
oil into the intake under higher manifold vacuum levels.