A pain point with React is large data structures. To re-render (assuming class components), you can setState with the changed property. For example if your state has two properties named foo and bar, and bar has changed then you call setState({ bar: newValue }). This works if you have simple properties. What if you have large complex data structures, and you need to modify a property deep down inside? Then you can make a copy of the data structure, then modify the field in the copy, then call setState({ bar: copyOfLargeObject }). But it is tremendously wasteful to make a complete copy of a large data structure!

A workaround is to not make copies of large data structures. Just modify the large object directly. Then just call setState({}); That's right... setState() with an empty object triggers a re-render. Now you don't even have to store the object being modified in state. You can hold the large object in a member field of the class. So even though your component is stateful, you are not telling React what your state fields are - you are managing it yourself. At this point, React's programming model has broken down.