This isn’t a sink! It’s a “hotel pan” – see my previous reply to @Gully_Foyle
Now that I’ve got my nitpickiness out of the way, your approach is valid for my case - and for sinks - and for door/window components, and for many other purposes. But it is, I think, too complex for what I’m trying to do. Like many things I do, I always think about how other people might use the tool I’m creating. Which means I don’t like this approach for a couple of reasons:
For my own use, I don’t need that level of complexity in handling the component. I can live with cutting only the top face of the counter as a cutting component does naturally. That way, I can still move it around and the top cut will move with it. Should I ever get to the point of having to present a fully detailed model, I can create a section plane of the “back cut” on the same plane as the bottom of the counter, copy the resulting rounded edge rectangle from the hotel pan, edit the counter component, paste the rounded corner rectangle in place, then delete the face it creates.
As an uploaded component in the 3D warehouse, my target audience would most likely be the SketchUp Make (not Pro) user who is trying to do a fairly quick concept model. I have lots of friends in the Tiny Home community who have installed Make for just this purpose. They won’t be bothered to learn enough of SketchUp to realize that “cuts only 1 plane” is a problem, and when it rears it’s (IMHO ugly) head, they’ll use something else rather than learn to change the counter depth to match the “back cut” component, nor to then explode it.
I have a tendency to go off on tangents that take me away from the basic task I’m trying to do, which in this case is modeling my idea of a group kitchen, This is such a tangent. I’ve determined that making my hotel pan component function as I wish it would is taking too much time away from the basic task, so I’m abandoning further work on perfecting it. I’ll live with it’s imperfections.
I reserve the right to raise the idea of a “cutting envelope” as an enhancement of cutting planes in a further topic, perhaps in the Developer/Ruby API category or the “Feature request 2017” topic (which I haven’t seen started yet, although I haven’t looked very hard!)