Did you ever walk quickly into your kitchen in the dark and did you have to learn the hard way that the dishwasher was open?
Did you have "only" a bruised shin or did you even fall down?
The Warning Lamp is supposed to protect you from that.
Opened dishwasher doors, especially in dim lighting, are a real tripping hazard. While there are devices with an interior light that is turned on when you open the device (which is great!) the vast majority are not equipped with such a thing.
A small LED lamp with the following characteristics
With the help of the sensors, the lamp is only switched on (and possibly beeps), if
If nobody moves any longer in proximity of the appliance, the lamp is switched off again.
Depending on the room situation, one single lamp (on the left or right side of the door) will be sufficient. But the safest of course will be two lamps; one left, one right.