When you do not care about the order of elements. Maybe you want to check how many enemies remain in the level. Or you want to destroy all traps. Or your backpack falls into lava and you lose all items. Still, there’s usually a more efficient way to keep track of things but GetAll can be a (clunky) shortcut.
Folks sometimes use GetAll when they are 100% sure there is only 1 thing they need to get, it’s lazy but hey, it does work, indeed.
Also, read the tooltip of that node, it comes with a warning.