I thought metformin was prescribed to reduce insulin resistance and metabolic syndrome in people with a BMI over 27, regardless of type of diabetes. I was never on it though, as my GP at diagnosis thought I wouldn't benefit from it as I hadn't any particular signs of insulin resistance or metabolic syndrome nor did I fit the BMI figure.
It is often prescribed to reduce insulin resistance in women with PCOS.
I have never heard of metformin as a help for micro vascular problems but then I'm not a doctor.