Why do scrollbars revert to original scroll distance when mouse is dragged sideways too far?

When dragging the scrollbar using the mouse, the contents of the scrollpane move up and down as the bar moves with the mouse. But if you keep the mouse button held down, and move the pointer sideways for about 100 pixels (tested on Windows machines), the scrollbar goes back to its location before being dragged, and the scrollpane with it. Moving the mouse closer again will make the scrollbar follow the mouse again. Is there any benefit or explanation for this behaviour from a UX point of view?