GP's claim is a little too strong, but in my experience most uses of `useMemo` / `useCallback` are only necessary because people define things in the wrong scope, or write giant spaghetti components with 15 different props and no internal structure. The best memoization technique is not calling things repeatedly in the first place.
I find it necessary for a lot of different types of patterns that optimize performance. See the very recently written beta react docs, they go over this quite well.
In general, I think it's always a mistake to tell people "don't use this tool because you may shoot yourself in the foot", best to explain the when and why. But I do have a problem when the tool has just stupid defaults that make it harder to use correctly in the first place.
> I think as developers, we tend to overestimate how expensive re-renders are. In the case of our Decoration component, re-renders are lightning quick.
Certainly it's there for a reason, and you may have expensive operations, but in my experience developers reach for useMemo much too early and often, and it just adds complexity to their functions. The cost of checking the parameters for changes adds overhead that may be more expensive than just re-doing the "expensive" operation. My rule of thumb is if the operation is less than O(n) where n < ~5000 I don't reach for useMemo.
There have been some benchmarks done on this, and when it pays off to use.