When would you use `useLayoutEffect` instead of `useEffect`?

I check whether CSS, intrinsic layout, or a declarative browser API can remove the measurement entirely. Layout reads followed by writes are batched to avoid repeated forced layout, and ResizeObserver handles later size changes when appropriate. Server rendering cannot perform browser layout, so the initial markup needs a stable fallback that avoids hydration surprises. I validate with a performance trace: the goal is not merely zero flicker, but a bounded pre-paint critical section under realistic content and device speed.