More clarification on updating Objects in state

here in the current beta docs of updating objects in react, we are just told to treat objects as read only and never try to mutate them but what are the exact tradeoffs if we try to mutate the existing state Object, i am quite confused and may be this requires a brief explanation

Like i have a sandbox below where it tries to just mutate the object directly and it works as expected

https://codesandbox.io/s/kind-poincare-k4g8uh?file=/App.js

從連結的 beta 文件頁面開始，更新 state 中的物件，並檢視展示直接 mutation 的連結 CodeSandbox 範例。釐清 mutation 現有 state 物件與將其視為唯讀之間的確切取捨，讓頁面說明為什麼建議的方法很重要，同時處理這個看似能運作的範例。