[wk_end]

I think it’s more that the React team’s way of articulating their idea of what a “side effect” is changed than that their idea of what useEffect is for changed. The examples of “side effects” in the old docs are all cases of “external synchronization”. People found the old terminology misleading because they came with their own preconceptions of what a side effect is, so they changed their pedagogical approach. The technical details haven’t really changed, just the presentation.