It does, if you say "expand desktop" instead of "duplicate". Obviously. Depending on how you lay the screens out there can obviously be regions that are off-screen, that would confuse an app or two (e.g. imagine a 9-digit phone keypad, one display occupying regions 1 and 2, another regions 5 and 6. An app might think to start with its top edge at the off-screen region 4, and its bottom half in region 1, requiring one to hit Alt-Space, M, to lock the window titlebar to the mouse.