Why are some T1s using Metformin?

Notice that quite some T1s in UK and on this forum quote in their signature that they take Metformin.
Why is that, as they also appear to take insulin at same time?

 

Thx Tim, so also Type 1s?? (sorry for asking, just to be sure I get that right)
And is it then becoming more predicable the insulin dose needed?
Reason I question for type1s is that since the Type1 already take insulin, whats the issue then if 3 or 4 units are required, as you already take insulin anyway. I suppose that taking Metformin do include some inconvenience and potential risks/side effects.