There is no 'bounding rect event'.

I can only assume you mean the boundingRect() function is called. The computer doesn't have magical intuition that allows it to know that two items don't overlap, it has to calculate it. Using bounding rectangles is the efficient way to determine whether arbitrarily shaped items possibly overlap (or collide if animated), which is necessary to drawing the view. Only if the bounding rectangles overlap is more expensive work done to determine the actual shape of the item should it be needed. In short, calling boundingrect() is not unnecessary work.

If you are worried about efficiency then don't do anything inefficient in your boundingRect() implementation. The bounding rectangle is generally immutable so you can cache the value.