With the addition of `React.memo`, is it still the recommendation from the React team that we only use `React.PureComponent` and `React.memo` in places where we profile and identify performance bottlenecks?

I seem to remember reading that adding something like `PureComponent` or implementing `shouldComponentUpdate()` can actually slow things down due to the cost of props/state comparison?

Either way thanks for another great release team! Suspense has me super excited!