Ok, an example - 24 keypresses have a certain effect and if that is the case we should do actions A and B, 16 other keypresses have a different effect and only action B should be taken. Currently I have to add a Set global variable to each and every one of those keypresses and if the order or such needs to be changed go through them again. Action B is reasonably extensive so doing it on any keypress would be wasteful.
I suspect plenty of other uses could be found, such as, say, changing things in a settings screen, etc - you could just add a single save event at the end if there's been any activity in a given group, be it clicks, keystrokes or something else. Or, the player gets damaged by one of umpteen different enemy families, each one with different impact fx, etc, but in the end you check but this one thing for a screen flash for damage. And so on and so on.