I've run one on my car since it had about 200 miles on it and it now has 18,600 miles on it. I've tried out various different ones and right now I have a Bob's separator on it. I've run the Bob's the majority of the time and it's probably my favorite of all of the ones I've tried.
I think they are beneficial even on the NA cars. My fiancee has an 07 Mustang GT that started smoking on startup at about 14,000 miles. People on the forums suggested installing an oil separator on it to stop that and that is what we did. It now doesn't smoke on startup.
I know when I originally pulled off the PVC line off the car, it was soaking wet with oil at the intake so you could tell it was pulling a lot of oil through the PVC system. Even on my 14 GT when I first pulled the line off, it had liquid oil at the fitting on the intake. I still would get this situation when I was using some other catch cans that were less effective.
Obviously it won't kill your engine but I like keeping that stuff out of my intake and throttle body and is why I run one.
2014 GT, Sterling Gray, base model, Automatic
GT500 AB, GT500 OTA pipes
Bob's oil catch can
Ford aluminum finned diff. cover
Ford all weather floor mats
Ford trunk liner and cargo net
Ford locking gas filler plug and wheel locks