One example of a reason you might want such an element to still participate in layout is to use that element as an area highlighter. Or you might make it a scrollable section; subgrid makes sticky-header tables rather trivial to implement now.
[0] Well, I can't remember right now if it's unstylable or if its height just ends up zero, but either way, it might not be what you expect.
That’s why subgrid ends up filling a different niche: you preserve the DOM structure, preserve accessibility semantics, and still let the children participate in the parent’s track sizing. It costs more than contents, but it avoids a lot of the accidental side-effects that show up once you start mixing layout, semantics, and interactivity.
Adrian Roselli is an accessibility expert who has done extensive testing and written up his findings: https://adrianroselli.com/2022/07/its-mid-2022-and-browsers-...
This took two seconds to make https://codesandbox.io/p/sandbox/5ry4rl
I do agree though that subgrid makes the HTML more readable though so I'm all for it.