As ever, it depends on your use case. If you're rendering 20 TODO items then who cares?

If you're rendering thousands of items on an SVG data visualisation, sure it matters.

You can tell it matters because otherwise React wouldn't have implemented escape valves to improve performance, like shouldComponentUpdate.

You can get around this by using persistent data structures with lenses, which is how Elm works. Then it's just reference equality checks as you go down the tree, which is inherently faster.