Earlier quoted context omitted.
If the thin widget is directly against the edge of the viewport, maybe. If it's literally anywhere else on the screen , then no, Fitts's Law applies, and it's a bad target. It has height but no width . This is especially true for those with motor or visual handicaps, or both. It's damned near unusable even with very modest levels of distraction or other factors, e.g., using a device as a passenger on a moving vehicle…
> If the thin widget is directly against the edge of the viewport, maybe. It is. Visually there's space between the scroll handle and the window edge, but if you actually point the cursor in that space it'll highlight the handle.
I guess thinking about it this is a very reasonable compromise, but it feels weird to start scrolling up and down with a cursor that shows a left-right arrow and that is technically pointing outside of the scroll bar.