Steamroller is a good option. It allows to automatically unwrap and flatten mappings on the channel of your choice on all selected objects. It’s a max script. http://www.scriptspot.com/3ds-max/scripts/steamroller.
I prefer to flatten mapping everything and use overkill lightmaps resolution and lightmass settings to compensate and get great results. Just quicker that way. If a mesh is too complex for a single uv map, I’ll break it into multiple parts and STEAMROLL every single pieces. It’s all automatic so it doesn’t matter if you have to unwrap 1 or 25 objects! This is such a time saver!