The Great Western Schism, as opposed to the Great East-West Schism, had a profound destabilizing effect on the faith people held in the institution of the Catholic Church. Most of all, it seriously deteriorated the prestige and assumed authenticity of papal power.
Because the crisis of the schism surrounded the existence of multiple simultaneous claimants to the papal throne, it created a split in allegiances, especially among Catholic European rulers. For example, France, Aragon, Castile, Scotland and Savoy supported the pope enthroned at Avignon, which was under the thumb of the French king, whereas England, Hungary, Portugal, the Holy Roman Empire and the Scandinavian states backed the one residing in Rome. Even individual cities, such as Bruges, developed different factions, ones that often viewed each other with fanatical hatred.
In addition to weakening the appearance of the papacy throughout Europe, the schism also inspired greater resentment towards it, causing vast numbers of Catholics to view its actions and motives with unprecedented suspicion. Additionally, because papal leadership failed so catastrophically, some Catholic thinkers began developing the conciliar theory, which advocated for a council representing all of Christendom to be the highest governing agency of the faith, creating an entity that would even outrank the pope himself, in theory.
Ultimately, the fallout of the Great Western Schism directly anticipated the troubles and grievances that spark the Protestant Reformation, which historically followed less than two centuries later.