We I suppose it depends on why manufacturers designed it to vent in the first place! Is it just for engine to breath or is it partially to clean crank and rockers aswell by removing vapours and gunk out of the engine,so therefore not back into the engine and obviously not onto the streets and can't expect everyday people to empty a catch can when necessary,so they vent to intake where most of it probably gets burnt off,leaving less gunk than if directed back to engine/sump