The more "typical" use for a feature like this is drawing tablets and touch screens. You don't necessarily want a touch/drawing tablet input to move your actual "main" mouse cursor.
That’s unrelated. The typical device will only ever have one seat. From Wayland core, that seat may have a pointer, keyboard and touch; and from tablet-v2 <https://wayland.app/protocols/tablet-v2>, you can add tablets and their tools and such, all still in the one seat.
Interestingly, for me this usecase isn't typical at all. Ever since I switched from X11 to Wayland (on GNOME) I've had the bug that when I'm drawing with my Wacom tablet, there's two mouse cursors and the tablet doesn't influence the main cursor anymore.
I thought this is a bug in the Wayland implementation: I find it utterly unintuitive to work like this. (I just have no idea with whom to file a bug report, which is why I haven't.)
Are you implying that this is intentional behavior?