I see that symbol catalogs have both fractal and smooth polygons. Is this because it is to accommodate bitmaps for fills that a smooth polygon is better to use than a fractal one? Or can they both be used for that. I am trying to finish up a style for the Harnic Regional maps and this is my last stumbling block as a fairly new mapper.
It's just to accommodate different mapping needs. Sometimes you need a smooth polygons, at other times a fractal one. Fills doesn't care if it is one or another.
You can use any bitmap fill you like with either smooth or fractal polygons. The smooth or fractal choice is about the nature of the shape you wish to draw. Most drawing tools appear in pairs - one smooth and one fractal per fill. Here is a quick example from the set I am working on at the moment.
The only one I haven't duplicated in this fashion is the Terrain, marsh island. This is because I can't imagine there ever being a need to generate square marsh islands. But this doesn't prevent the user from duplicating the smooth tool and making a square version if they wish.