The Windows key is default to launch Unity’s dash home. In some work situation, keyboard doesn’t have a win key. So we need to change shortcut key for launching the dash and fortunately
gconf-editor can do this.
First install gconf-editor via Software Center, or this command:
sudo apt-get install gconf-editor
gconf-editor (Configuration Editor), navigate to “apps -> compiz-1 -> plugins -> unityshell -> screen0 -> options”. At right box find out “show_launcher” and change its value to what shortcut key as you want.