Need for ViewParent.disallowInterceptTouchEvent?

Views may at any time invoke disallowInterceptTouchEvent() which will prevent parent views from handling touch events. In short, what is the need for this API? I see that lists use it when a scroll is initiated, but why? The list wou开发者_开发技巧ld still receive ACTION_CANCEL if a parent view intercepts the event, so why would it specifically want to block onInterceptTouchEvent on parent views?