Why is grievous wounds needed as a mechanic in league?

It’s one of the most obvious forms of what we call a “release valve.” These are systems elements (often item passives or actives) that a player won’t normally value, but can opt into when they face a particularly daunting challenge. Grievous Wounds isn’t usually needed, but when you’re playing against a comp with Mundo/Soraka, it’s one of the most valuable things you can get in the item shop.

Release valves serve a few purposes. They allow for intellectual mastery, whereby a player can see a state in the game, and make a powerful reaction that has a clear impact. They also create room for us to push strengths. Healing champions would need to be much more limited in a world without GW, for example. Most champions on their own don’t push the need for a release valve, but when comps can stack similarly sharp characters, release valves allow opponents a way to deal with dramatically skewed power.