When in the overview, if you move the mouse cursor over one of the
application launchers in the dash, all the unrelated windows are dimmed
both both in the window view and in the workspace view.
It helps to easily understand whether or not there are already opened
windows for this application, and where they are. It can also help in
differentiating the windows in the overview (sometimes the thumbnails
aren't precise enough to easily know which thumbnail belongs to which
application).
https://bugzilla.gnome.org/show_bug.cgi?id=657315
76229a3601