Allen,
The PCV valve relieves pressure and if you just use a breather you can get
oil fumes that will eventually make a mess on the top of the valve cover. We have a man here with a $100k plus Cobra that is now having a PCV installed because of that very thing. I know the people that built my stroker put a PCV valve in it and told me to be sure I keep it clean to take away that pressure. My big block also came from the factory with a PCV valve.
Ron61