Reset static lights - EDIT: static skylight doesn't affect world

But the most important thing is that I didn’t understand how light works. I mean, with static lights ALL the lighting informations should be rendered into lightmaps, right? So when I delete all lightmaps the light should return to the light previous of the bake (see my first screenshot). So what are those strange shadows

Also I am very confused about the preview mode of static/stationary lights of UE: what is his utility if after baking lights look COMPLETELY different from the preview?