Set Timer By Event node doesn't cause the event to be triggered

But game instance exists throughout the whole game lifetime. Why do we need to check if it is valid?

And wait, you’re saying that SetTimerByEvent node reuses the same timer on each call, then why does it give a new timer handle each time it is called? (As it is seen in ClockworkOcean’s post here: Set Timer By Event node doesn't cause the event to be triggered - #22 by ClockworkOcean)