D+B works with shading not texture. There is a big difference. Yes it can work with texture, but I think that one of the reasons that people are confused with the way the technique works is because of the definition given.

D+B, or softlight retouching is used to preserve texture in ways that the stamp tool and /or the healing brush can not possibly achieve. Some will say that if you use the mentioned tools set to lighten or darken only it will achieve the same effect.

It doesn't. Ever.

It only succeeds in flattening out an area that then needs to be "doctored to look right".

Nor is Soft light retouching meant to ever be a quick solution to fixing a file. No matter how good you might become at it. It would still mean that you rushed something and it is not at its best.

I have been using the softlight method for nearly 9 years now, and I still take my time and to get it right. If that means it takes me 4 hours on a file that is acceptable to others then so be it. It will then look above and beyond when I am done.

D+B(softlight to some) should never be described at the same time as the word texture. It is to misleading. More than not, it is a drawing technique. When you draw you are not putting texture onto paper or canvas. You are adding shading to the surface. A surface that already has texture that your shading is meant to bring out.

I get asked all the time why I use a softlight layer with a neutral grey fill. Then I get asked "why I use a grey fill and why not leave it blank. It achieves the same thing". And the final question in the series is always "Well I just use the dodge and burn tools on a duplicate of the pixel layer"

To start, the dodge and burn tools that reside in the toolbar are destructive tools. I know that I will get some arguments about this, but think about it. These tools are used to adjust exposure, not shading. Exposure is meant to be a means to capture/adjust a whole and not a portion. And yes, you have pulldown menus for highlights, midtone, and shadow, but they take a while to get the hang of. I see a lot of people using a midtone dodge brush set to 80 on a highlight area (for example). There is just no way to accurately set what that exposure is truly supposed to be at nearly pixel level retouching. When used right, and for the right problem, the dodge and burn tools are great.

Why do I use softlight for my retouching? As opposed to overlay and hardlight? Softlight takes a little longer to achieve what the others do, and with a lot more pressure and density with the brush. Again, it comes back to the level of control I like to have over my tools. Overlay moves far to fast for me and hardlight is to harsh. These two blend modes, for nearly all corrections, are better left to overall moves with a layer mask(or no mask). or within a selection.

So, that leaves me with why fill the softlight layer with a neutral grey fill? Sometimes I use a brush that has such a small amount of pressure and opacity that it is nearly invisible on a transparent layer. The grey makes it stand out rather easily which is good for workflow. The grey also allows me to see how much I have done to a particular area without having the need to use an eyedropper to measure it. The grey also allows me to fairly easily eliminate a portion that I don't like any more without having a whole in the document.
The grey also allows me to blur or sharpen any of my drawing. Or use any color correction methods on it. The list goes on and on.
But I have yet to come up with one good reason not to use the fill.

One more thing before I sign off on this. I don't really understand why there are so many people out there in the retouching world that insist that D+B(softlight) retouching has to be at a pixel level. It is not necessary to zoom in to whatever view the resolution of the image allows for viewing individual pixels. I rarely if ever go above 150% view. Most of my work is done at 100% or less. The further in you zoom the more work you have to do. Kind of like not seeing the tree for the forest. You loose focus on what you are trying to achieve.
The important thing is to get the hard stuff done at the bigger views and then progressively zoom out and using a larger brush and lower opacity, brush out some more.
Better yet, I keep two instances of an image open all the time. One is focused(set to view) the most I can of an image. While the other one has the zoom factor I need to do my retouching. The larger updates as I go along so I can see what looks strange or where I need to go next.

I hope this clears up some of the way people are thinking about what D+B/ softlight retouching is.