whats hte advantages...and dis?

None of either for the most part. Just there for looks. Supposedly they help the engine vent bad gases or something but the general concensius is that t does absolutely nothing, I have one but it is purely for looks.

Please correct me on this. But didnt't the PCV replace all the Oil Breather Caps that were located on the valve covers back in 1968??? This was the start of emission restrictions.

Some engines use the PCV as the oil cap, and some have it seperate. The 3800 series 1 SC has it seperate. You can see mine here (old cap, not the breather):

Right, but I was under the impression that all engines after 1968 were "closed". Meaning all engine oil fumes would be directed back into the carburetor(air/fuel mixture) where it will be burned for a cleaner emission. I would assume that if you put a breather element in place of the oil cap(on our 3.8L engines) you would definitely generate an SES code.

Even if you threw a code, I doubt it would hurt your car in any way. But I would be interested in learning the specifics on this.