Backlighting is most of the time done wrong. When set to an intermediate intensity, most keyboards turn the LEDs on and off very quickly so they emit less light overall. This is called PWM (pulse width modulation).
The result is horrible. When your eyes go from one point of the keyboard to another point, or to the screen, you can see the multiple images of the keyboard PWM creates on your retina. It is utterly distracting.
So backlighting can be used on only one setting: full throttle. Because in this case the LEDs stay on all the time. Unfortunately, full light is generally not the right setting, depending on your environment.
The only keyboard I know of on which backlighting is done right is on the MacBooks. They don't use PWM to dim the light, and the illumination can be set to adapt automatically to the ambiant light. That's backlighting done right. It's useful on a portable computer that you may use in badly lit places.
I guess there must be some mechanical keyboards that do backlighting right, but your best guess when you purchase one is that it will NOT be done right, because PWM is much easier to implement that any other method for dimming the LEDs.
I'm not even talking about the fact that keys designed for backlight keyboards are of poor quality, and that replacing them deceives the usefulness of backlighting (unless you replace them with some other poor quality set of backlight compatible keys - WTF!?).
I used to be a fan of backlighting, but experience has taught me that it is generally a pain. Only if you have a real good strong reason and you really need it you can take this into consideration when purchasing a keyboard. If it's not an absolute requirement for your use case, this is a point you can ignore.
