How does insulin work on the body?

I've always thought that high blood sugar causes weight gain.
This is natural when you eat a lot of junk and your blood sugar rises.

What about when you use HGH? Increased blood sugar does not come from more calories.
Insulin works well on the body by releasing the sugar into the muscles and the body then uses the sugar as energy.
When blood sugar is high, the body uses fat as energy.
Is this correct

Which blood sugar is best for maximum weight loss?
Best to lie in high normal range 6nmol/l / 100mg/dl or low normal range 4nmol/l / 70mg/dl