If I change the brightness by scrolling the wheel on the battery icon in the notification area, “0%” is still visible. But if I press the brightness down key on the physical keyboard, pressing it when the brightness is 5% turns the screen off. That is, nothing is visible. Is this the intended behaviour?
Please think about it: If you turn off the light, is the intended that it should be dark then? Even if the backlight is off, that does not mean that the screen is off.
I don’t know, I cannot think of any useful situation of the LCD itself being turned on consuming the energy and its backlight being turned off so nothing is visible. And I have never seen other operating systems where if I set the brightness to the minimum, the backlight is actually turned off.
I think it makes more practical sense not to go below the minimum brightness.