Hmmmm I think I have found the side effect.
If You have / use / like the noblank.sh script in Your autostart then this command will render it useless.
Example - system starts and noblank script is fired up - it's purpose is to not to allow screen to go blank. I ran the command and screen went off for the night. In the morning I moved the mouse screen came back on but when I left the room to get some coffee and "breakfast" and came back the screen was off again.
Re-running:
xset s off && xset -dpms
should do it... I am thinking about the "ON/OFF Switch" widget... Must have a look if it's still in the repo...
Regards.
Andy