I’ve found that no cooking utensil I’ve ever used is hard to get clean if I soak it overnight with some detergent in the water. Whatever was cooked, baked, or burnt on softens and easily brushes away. I don’t know these Le Creuset Grill Pans, but they are enameled, are they not? If so, the water should not hurt them. I would not even bother to try cleaning without first soaking.
I purchased a cast iron skillet on the basis of expected durability. To me, this skillet appears to have the surface left by the casting process. It has a made in China sticker on it. I know cast iron can be polished, probably to a mirror finish. I wondered if smoothing the interior before seasoning could lead to the skillet requiring less oil/grease for cooking.
The internet provided information I never guessed, especially the claims on this site that "proper" seasoning produces an excellent, permanent, non-stick surface. I have not found the information I wanted, however, perhaps because I did not think of the proper search terms.
I see mention of using 80 grit sandpaper on "unpolished" cast iron. It isn't clear to me, however, if this sanding recommendation is to actually change the metal's surface or just to remove anything that might coat the metal. I don't think 80 grit will produce an especially smooth surface, although it probably could be smoother than what I'm starting with, assuming enough sanding.
I also saw the post about Lodge marketing a rough finish as a way to improve the eventual non-stick qualities by providing more surface area to season. There was no information as to whether this is good or rather backwards, however.
Will the skillet ultimately have a better non-stick surface, or be better is any other way, if I polish the interior before seasoning? I'm aware this could be a major undertaking, maybe more effort than I'm willing to give to it, but that isn't part of the question. Only "is it a good thing to do?" is being asked. However, if the undertaking is worthwhile, any suggestions to ease the effort are also appreciated.