Currently our only reasonable way to have complex menus / GUI's is to store them in global layers and toggle their visibility. This can become cumbersome after some time and is difficult to keep them consistent throughout all layouts. My project currently has 17 layers just for GUI & GUI effects/accessories, and I expect more on the way.
With layer X/Y offsets, I could just put all of this on a single layer instead and offset that layer by the screen width/height to reveal different menus & GUI elements. Paired with fade transitions, players will be none the wiser. This seems to be a sensible method until Prefabs / Scenegraphs are added.
I'm sure there are other uses as well. We could have menus or other object groups slide in, like Zelda's pause screens. Perhaps even aesthetic things like a background that sways up and down like you're on a ship, or layer-specific screen shaking.