Grand Rituals is a system agnostic tool for big magic that can be applied to many types of tabletop roleplaying games. It can be used in magical situations when you desire results that might exceed the capabilities of your character.
Grand rituals might emulate the effects of a higher-level spells for characters without the power to use them, they could be used to elevate the scale of an already potent spellcaster, or even overcome the laws of gods and nature to do the impossible.