I assume that when texturing environments, one or several textures will be used, and the UVs of the environment geometry will likely overlap on these textures, so that e.g. a tiling brick texture can be used by many parts of the environment, rather than UV unwrapping the entire thing, and having several areas of the texture be identical. If my assumption is wrong, please let me know!

Now, when thinking about baking lighting, clearly this can't be done the same way - lighting in general will be unique to every face so the environment must be UV unwrapped without overlap, and lighting must be baked onto unique areas of one or several textures, to give each surface its own texture space to store its lighting.

My questions are:

1. Have I got this wrong? If so, how?
2. Isn't baking lighting going to use a lot of texture space?
3. Will the geometry need two UV sets, one used for the colour/normal texture and one for the lighting texture?
4. Anything else you'd like to add? :)