The advantage of a catch can is that you will keep oil (which has an octane rating of like 60) and residual combustion gases from entering into the combustion chamber therefore reducing detonation.
The down side is you will not have vacuum in your crankcase which supposedly helps piston rings seal better, also your oil will break down a little faster.
Now, personally I run breathers on my valve covers and have never had a problem with rings not sealing (I run gapless rings, though) and I change my oil very often anyways so it is not an issue for me. Personally, keeping all those gases and oil from entering the motor is most important.
You can go half way like Rusty did and get a separator to keep some of the oil from entering back