The most effective laws are those one follows without being conscious he is doing so!
It took me many days to realize that this is a convention all MS Windows applications follow but APP don't follow. This is not a gadget to entertain or distract the user, it's so deeply inscribed in our mind that, when a program can't answer and the hourglass is not displayed, we feel very uncomfortable but are not always able to say the reason...
I ended having Windows Task Manager always on the screen when I use APP but could not say exactly why it was needed.
When using Photoshop or any other application, the hourglass is displayed in each occasion where said application can't answer to my key strokes or mouse clicks. There is no escape to the hourglass convention.