That selection shift when dragging on unselected objects can be pretty useful for arranging simple objects other than control points.

For example here it comes into play when just dragging these lines to snap them together:




That's just doing 2 drags, no other keystrokes or clicks are needed. That's what is enabled by shifting the selection when dragging on an unselected object.

If that was removed, then this simple sequence above of just dragging some lines to snap on to other things would require an additional click in between in order to clear the selection.

- Michael