It was one of my most wished-for features when I moved over from Lightroom, because I was used to the “masking” option in Lr that works in a similar way. So, when it arrived in darktable I jumped on it in an instant. It’s now part of my basic processing style that I apply to all images, with a detail threshold set at something like +75. That just sharpens most obvious edges but leaves most of the image unsharpened, which I prefer. I can then tweak it to every individual image.
One thing I’ve wondered though is whether feathering should be used with it or not. I find most dt masks need feathering, but not sure about the details threshold ones. Anyone have any thoughts on that?