Its actually one of the first recommendations/ mod to do for a fast and cheap performance boost, along with trimming the gasket to match.
Same goes for the exhuast, the gasket and manifold for the exhaust are restrictive from factory.
Although leaving the intake side a little rough helps with the atomization of the gas and air mixture, which improves performance
The exhuast side is better off ported and polished, a smother the exit, the better the performance