React useCallback vs useMemo — When You Actually Need Them

React is a UI library for building components, while Next.js is a full framework providing routing and rendering strategies. Regarding performance, useMemo caches computed values and useCallback caches function references. Over-memoizing can lead to slower interactions due to increased comparison work, as shown by the React Profiler. Developers must decide between a framework or a library based on project needs, avoiding the mistake of treating Next.js and React as direct competitors in development.