While you can safely shoot rifled slugs from a rifled barrel, this is NOT recommended.
Rifled barrels are intended for use with sabot slugs ONLY.
Shooting rifled slugs or shot will cause the barrel to lead up BADLY, and the lead is hell to get out.
Due to the incompatibility of rifled slugs and the rifled barrel, accuracy will be terrible.
In the smooth bore barrels, you can shoot ANY standard rifled slug, birdshot, or buckshot.
You can even shoot sabot slugs, but due to them being designed for rifled barrels, accuracy is usually bad.
So, rifled barrels are for sabot slugs ONLY.
Smooth bore barrels are for anything.