Persistent map size increases when saved with sublevels loaded

I have two questions.

  1. When I save my persistent level without sublevels loaded, it’s about 12MB. But it becomes 190MB if I save it with sublevels loaded. Why the difference? What’s the correct way to save? In both cases, a packaged game seems to run fine.
  2. I recently dabbled with World Settings | Force No Precomputed Lighting (on) and Project Settings | Rendering | Allow Static Lighting (off) to disable any light backing in my map. After some experiments, the editor ended up generating MyMapName_BuiltData.uasset files for the persistent level and each sublevel, which weren’t there before. What are they? With static lighting off, what other data needs to be built? How can I get rid of them (and their references in umap files)?

Thank you!