[brundolf]

Re-rendering JSX subtrees is the main performance bottleneck in the majority of React apps. I should add that our decision includes the decision to start adding React.memo() to all components; otherwise, yeah, the benefits in most cases would be pretty small. But with React.memo(), useMemo/useCallback makes our components dramatically less likely to re-render, which again is the single biggest thing you can do for performance in most React apps. The difference is usually not perceptible on high-end dev machines, but a significant portion of our target market uses lower-end mobile devices to visit our site, so being performant-by-default is valuable to us.