A few mm off would likely not be an issue. But I'd have to agree that bad thing will happen with a full 10mm offset. I would not want to see much more than a 3mm offset if I were setting up my own SS bike. And at 4 to 5 mm I'd be swapping stuff around to make the offset less even though likely the worst effect would be a slightly reduced chain life. But at 10mm I'd not be surprised if there were not some snapping as the chain tries to climb up and over the teeth but fails and drops back down again.