Avoid 1 sided meshes if you are using lighmaps, light will leak. Also avoid making your scene from tiny modular elements, Lightmass doesn’t handle modular pieces that are flush and tiling well, and people can tell if scenes are made from lots of tiny repeating elements. It affects how scenes can be put together.
Though, you are right about what you said, I’ve been looking through the learn section and people just cover up the seams with extra things and depending on how dirty the place is, the seams dont really look bad. But im still look for the answer to my lightmap UV’s that you didn’t say anything about. Just wanted to know so I can UV map it correctly.
From that example, the floor seams are the worst part. The seams are pretty terrible and wouldn’t work for a clean look. But of course if your texture has a seam on the edge of tiling pieces, the seams are basically covered up.
Stretching lightmap UVs isn’t an issue at all, you can get away with a lot of stretching, and not have any artifacts show up. Extreme stretching can cause some artifacts on the edges of shadows, but it’s rarely an issue.