This is simply stronger local contrast limited to mid gray range by parametric mask:
It works in most cases without any additional adjustment (quick) and is mainly used to restore the local contrast lost by filmic’s dynamic range compression. But I don’t always have to use it.
It widens or narrows the dynamic range symmetrically. You can work with it quickly and, if necessary, use other two sliders to readjust it. I’ve mainly used it to widen the dynamic range, or in rare cases when the other two controls aren’t enough to compress, you can use it to compress even more.
For the narrowing of the dynamic range, I use the first two sliders first, because you can influence the areas that should be compressed (shadows or highlights) more directly for the corresponding photo.