This is fascinating.
Observant Jews (mostly, Orthodox Jews) do not turn lights on and off on the Sabbath, because doing so is considered work (because it’s “making fire”), and work is prohibited on the Sabbath.
So, imagine you make refrigerators for a living. Including a refrigerator that has a water dispenser on the front of it. A water dispenser that has a light that goes on and off, whenever you push the button that dispenses water.
Observant Jews would find this functionality useless, because by pushing the button that dispenses water, the light goes on and off.
So, what do you do?
Simple. Create a refrigerator with a built-in Sabbath mode. Light goes on, six days a week, but not on the seventh.