The answer
It controls when the value recomputes. Include every value used in the computation that can change. If you miss one, the memoized value goes stale; if you include too much, it recomputes unnecessarily.
useMemo in React Explained: What It Does and When to Use It
How does the useMemo dependency array work?
More FAQs in useMemo in React Explained: What It Does and When to Use It
useMemo takes a function and a dependency array and returns the cached result. On subsequent renders, if the dependencies have not changed, it returns the cached value instead of recomputing, avoiding expensive work.
When a computation is expensive and would otherwise run on every render, like sorting a large list or a complex calculation. Also to keep an object or array reference stable so memoized children do not re-render unnecessarily.
No. Memoization itself costs something, so wrapping cheap computations in useMemo adds overhead without benefit. Measure first and use it only for expensive work or stable references.
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