D-Lighting is good for?

I just don't get it. When should I use it and how do the different levels of low, med, high affect the overall image? I've experimented a little but never been happy with the output.

Balancing Photo Exposures with Nikon's Active D-Lighting from Nikon

Here's a Nikon article with examples of what it's supposed to do. I've never turned it On. Too many other solutions in post processing to achieve the same results if needed... I'm in the "less is more" camp when it comes to camera settings...

I turn it off because 1. it's easier to do a better job in post and 2. turning it off speeds up the files going to the card.

Are you shooting RAW or JPEG?

I've used it when taking jpeg photos of the local high school's drama productions. If you have a subject set in a high dynamic range with lots of contrast and the Active-D lighting is turned off, either the brightly lit areas will have detail while the darker areas simply blacken out (little to no detail); OR the darker areas will have some detail while the light areas have blown out completely. With Active-D lighting turned on (extra high for my preference), I am able to salvage some of the detail. The idea behind it is that when turned on, it allows more detail in the shadowed areas. For low contrast photos, you won't see much, if any, differences.

The problem is if you take a jpeg photo with it turned off (and are shooting a high dynamic range subject), when you edit the photo and raise the shadows, you will add noise plus the final result isn't quite as nice as if you had the Active-D lighting turned on.

It your subject has a high dynamic range, that's when you will really notice the difference while using it. Otherwise there is little difference. And if you are shooting RAW, it won't affect the outcome. I believe it is a setting to control jpeg results.