It reduces insulin production by the liver and also increases insulin sensitivity, so I would have thought that it might help reduce your doses. Just might need to be a little more cautious about hypos???? If you have problems with the dawn phenomena (blood sugar rise on waking) then it might help.
I was on a double blind trial for T1s taking metformin for a couple of years, but unfortunately never found out whether I was taking a placebo. The trial results weren't terribly conclusive, but it's a very safe drug and if your doctor is recommending it it's probably worth a try. I've been offered it but as I'm reasonably happy with my control at the moment I'm not bothering, though I wouldn't rule it out in the future.