Hardware 2D (2DS) vs. 2D (3DS)

[RodrigoDavy]

The slider does nothing to the parallax barrier, which is in a fixed state inside the screen. The slider just computationally moves the right and left images closer or further apart to decrease/increase the illusion of depth. When the slider is all the way down, the left/right images are identical.

Also, the parental control 3d toggle is functionally equivalent to turning the slider all the way down. (except it gives you a nag screen every time you boot an app)

I think you're wrong, the parallax barrier isn't in a fixed state. The parallax barier is actually a black and white lcd screen... When you slide the slider up and down the parallax barrier does stay unaltered, but when you slide all the way down the parallax barrier is deactivated, that's why you can notice a difference in the brightness when you switch to 2D and it also give you the advantage of having full resolution in 2D mode