How I use them: My big expensive mechanical keyboard collection is mostly using QMK firmware. For whichever keyboards I'm currently using, I have a git worktree per-keyboard.
I'm one of the weirdos that still holds on to mercurial as I genuinely prefer it's methods and workflow to git most of the time.
How the author describes handling work trees is exactly how they work in hg, and I find it enormously convenient vs the way that git by default really wants you to branch with work trees.