When workspace "previews" in the overview were just tiny gray
rectangles, it made sense to provide a way to move windows
directly between workspaces (by switching workspaces when dragging
a window to the corresponding screen edge). As the overview has
evolved however, the workspace switcher provides a good and
intuitive drop target already, so the alternative provided by the
screen edges is no longer necessary. As it also conflicts with
moving windows between monitors when using a vertical layout,
just remove it.
https://bugzilla.gnome.org/show_bug.cgi?id=660838
28c3e0693e