There's lots of catch cans in use by turbocharged subcompacts - civics, integras, etc etc. In many cases its just a bling bling thing. In some however, it is a legitimate device - in my Nissan, for instance, oil apparently will spew from the crank case breather if turbo charged - i.e.: a litre in an afternoon, and that will absolutely pollute your intake track and throttle body, as well as endanger the motor overall by fawking around with the octane level of the gas.
So - your cc breather goes to the catch can, oil accumulates in there (maybe a return line to the pan?), and air continues to the intake.
Like I said, in most cases its a bling bling thing.