I found mystery with 2d Lights in unity

Hello forum. Today i found intresting and mystery moments in unity. Bug or normal situation?
Please, see the video below, my question can be stupid without watching video. (maybe with video too xD)
That situation happens with URP, 2d lightning system and Unity ver 2020.1.5f1.

1. Before activating global light, every sprite on scene - black (all have Sprite-Lit mat). After activating global light - lighted with power of global (0.25 on video). BUT (!!!) if i switch global light target to "NONE" all sprites will be bright like they have Unlit mat, but mat still Lit, lol.
Is that normal situation?
2. On video we can see, global light without target layers still eat much fps, is that regular state? Or maybe exists any solution to reduce that impact?
Thanks for asnwers