Use Lazy State Initialization Pass a function to for expensive initial values. Without the function form, the initializer runs on every render even though the value is only used once. Incorrect (runs on every render): Correct (runs only once): Use lazy initialization when computing initial values from localStorage/sessionStorage, building data structures (indexes, maps), reading from the DOM, or performing heavy transformations. For simple primitives ( ), direct references ( ), or cheap literals ( ), the function form is unnecessary. ---