I use them a lot in Capture One, for more subtle adjustments (e.g. selective sharpening, clarity, etc.) so nice to see Lightroom users soon getting improved tools as well. Adjustments to selective parts of the photo forces us to think what is important about our photo, what is not important in the photo, what are we really trying to say with our photo, and I think it is good exercise.
I have to say though, based on examples I've seen on YouTube, maybe people rely on masks a bit too much (not so subtle adjustments). And yet at the same time, when they do decide to rely on them, maybe people are also not meticulous or careful enough when drawing them. Layers and masks are a powerful tool, but I hope with Lightroom people don't start getting too carried away with them and yet more careless with them at the same time like they do now using Capture One.