Some more context on why the PR doesn't make a dent in the existing benchmark suite: - existing benchmarking suite uses react 17 as the baseline, the new useInsertionEffect hook requires react 18. Additionally, the new hook plays a role in concurrent render scenarios also introduced by react 18, which the current benchmark wasn't testing. We made a new benchmark on react 19 in a worst case scenario that the new hook is designed to mitigate, we shared a recording of the before and after here https://github.com/styled-components/styled-components/pull/... with before and after links. = react 18 and later and its concurrent render mode uses cooperative scheduling techniques and tries to yield to the main thread and have your application stay responsive. You won't see a difference in flamecharts in the same way as typical perf issues, since the problem isn't that something is blocking main thread render and causing locks or fps drops necessarily. The problem is that background render takes much longer and risk hitting the deadline where it becomes sync. - it's notoriously difficult to write benchmarks that tap into concurrent mode behaviors in react, our own benchmark had to write css that escape the default styled components scoped selectors in order to get consistent bench results. - if it's the same speed as before in the react 17 benchmarks it means the new behavior and its fallback when outside of react 18 is working as intended and did not cause a regression. It's not reasonable for it to be significantly faster in all cases, the purpose is to prevent it from being extremely slow in Suspense, React.lazy, useTransition, useDeferredValue, <Activity mode="hidden">, startTransition, and other concurrent mode cases.