I think the point of it is consistency. Why were there two totally different pieces of UI (the lock screen and Notification Center) that both housed notifications but didn’t look or work the same? Why could you swipe to get to camera on one, but not the other? The point of of the Cover Sheet (thanks for rooting that out @Dj64Mk7), I think, is that the same functions, the same gestures, the same everything is available no matter where you are in the UI.
Ok I could see that as a possibility. But that seems like an awfully big step back on the notification side of things for the sake of consistency. And I still don’t really feel like it was a necessary change. The lock screen has been understood to be a screen where notifications are displayed when the phone is locked since literally the first iPhone was sold. And the Notification Center has been basically the same since it was introduced in iOS 5 as a place to view all of your notifications when the phone is unlocked.
Maybe this idea of a central Cover Sheet will grow on me as I use iOS 11 more. But Apple will really need to do some user education about this change, as it will be very confusing to people who are used to the lock screen being a lock screen. And I still don’t see why the clock needs to waste so much space or why the music widget is there and not on the widgets page. The consistency argument, while definitely the best explanation I’ve heard so far, still seems a bit flimsy.