Question about Lightmass Importance Volume (effect on level)

I’m building a simple level for a tutorial using assets from the marketplace.

I had one in the first tutorial project. I don’t have one in the second tutorial project.
Could this be why some meshes appear fine on one side and completely black on the other?
I also have a hard time seeing what I’m doing with some meshes and point/spot lights don’t work like they should.
Do I need one if I’m building an interior space with no windows?