Is increasing data rate useless or???

[eco_bach1]

I would assume it would have some benefit in reducing banding and artifacts in any area with large areas of flat color. A good test would be simply to shoot 10 seconds of a blue sky with a wide enough FOV so you go from light to dark.
Also guessing it might be beneficial when shooting green screen. has anyone done tests to confirm this?

[1%]

If you're talking about CBR, the encoder will pick higher qualities if set to larger sizes. It can't really control the data rate per se.

The difference between Q16, 0, -16 is big but -10 vs -16 people disagree on. I think it makes a difference. 120mbps video vs 40mbps video.