Unlike GNOME or Cinemon, there seems not to be a all-in-one point-and-click solution for XFCE. Multiple hacks are described around the net, but this worked in my case – a BeagleBoard displaying showcases.
DEBIAN 8.1.1, XFCE Desktop Environment:
1)
Deactivate the settings via the menu: Settings > Screensaver
2)
Edit /etc/xdg/lxsession/LXDE/autostart
@lxpanel --profile LXDE @pcmanfm --desktop --profile LXDE @xscreensaver -no-splash
becomes this:
@lxpanel --profile LXDE @pcmanfm --desktop --profile LXDE # @xscreensaver -no-splash @xset s noblank @xset s off @xset -dpms