I wouldn't say they do "nothing".
After 3000 miles.
It reduces oil blow by into the intercooler charge pipe and intake the intake manifold.
If your concern is preventing carbon build up on the intake valves you will be disappointed find out that is inevitable as it is a characteristic of direct injection engines since the injectors do not pass fuel over the intake valves any longer.
However the OCC still helps in keeping oil out of the intake tract in general.