5. If you are all in on optimization, if the polygon will not be seen by a user, get rid of it. Otherwise this will go towards the overall lightmap texture space which is a bit of a waste. Especially important for large polygons (floors/ceilings/walls) eg. if you have a ceiling and there are polygons on the other side that are never seen, get rid of the outside polygons. If you have a light source outside though and need the outside to caste the shadow (polygons are one sided, so light passes through single polygons from one side), then separate the top polygons and use that as a NON static model so it doesn't contribute to the lightmap.