This feels like a step backwards for me, too, and I love overlapping windows and never split my screen. The benefit of having multiple windows is that you can have different working contexts that don't overlap, which makes it easier to find the exact window you're looking for. But look at the screenshots in the article: you still get one web browser window, one calculator, one instance of every app. You can't split (say) the browser into Tabs for Project A and Tabs for Project B, or keep a calculation open for Project B then open a new one without destroying the old one. (Contrived examples, perhaps, but those are the only apps demonstrated in their screenshots so far. Imagine it with text editors.)