So let's say that you're playing a round of Metroid and you have to abruptly end your session for some reason. Maybe it's time to eat dinner, maybe your appendix ruptured, whatever.
But instead of finding an enemy to clumsily bump into repeatedly or taking an excruciatingly slow bath in a Lava Pit(tm), you could just pause the game (trust me, it's paused in this picture)
Then grab Controller 2 and press Up on the Control Pad + A
Done right, your game will end suddenly and you'll be taken to the password screen
Where you can jot down your password to continue on another day.