input - When is it a good idea to perform actions on mouse-down *as opposed to click/mouse-up*?

I've grown used to the GUI paradigm of pre-select on mouse-down, action on mouse-up. In fact, I rely on it, sometimes canceling an unwanted action after mouse-down by dragging outside of the click area and then releasing the mouse.

However, this is only an arbitrary standard, and may not be universal. For example, I noticed that in Microsoft Outlook's header pane, category selection occurs on mouse-down (and interrupts attempts to drag).

With the introduction of touch-oriented interfaces, the dividing line is even sharper. iOS automatically "retracts" finger-down events and converts them into drag-view events when the finger moves after finger-down.

What are some situations where it's preferable to take action on mouse-down? What sorts of actions are better this way, rather than waiting for mouse(/finger)-up?