Not always chamber-wise, exh.-ports sure,....but it's effect is temporary. Once fuel/oil/combustion residue bonds itself to the metal surface, it behaves as if You didn't do anything. If it's a mill that gets torn down regularly, it cleans up easier/faster, but a long-haul mill it's a waste of time IMO. Getting obviously jagged/rough/sharp features cut down, sure, always. But I've polished chambers & piston crowns 'til a gal could pluck Her eyebrows in 'em, and by 10K everything had a coat of carbon on it anyways, not heavy but just the same.....