IMO, "scroll here" should be the default action for clicking on a scrollbar. There are already good keyboard shortcuts for page up and page down, but there cannot be a keyboard shortcut for "scroll here". It's wasting the capability of the mouse to duplicate keyboard functionality when you could be benefiting from unique mouse-only functionality.
mrob · · focus · HN ↗
GTK gets this right, and Qt does not.
NooneAtAll3 · · focus · HN ↗
pgup behaviour allows for intermediate speed when line-by-line is too slow, while dragging is imprecise
mrob · · focus · HN ↗
That's two actions, while clicking is only one.