Flux is an aesthetic thing. It just tints the screen reddish to match incandescent lighting. If you wanted to remove blue light, which is what affects melatonin production in your brain, your screen would actually look very yellow.
Flux can go far past matching incandescent. I generally set it to get rid of the vast majority of non-red light when activated. Removing green is more benefit than harm because it overlaps the critical blue range somewhat.
