[mrloba]

In general a function component does a lot more work than a class render function. Some of it is just about handling cases that we probably should have done with classes as well, but often didn't. The result is that everything must be carefully memoized (or not, it's sometimes hard to predict). For example, should you memoize a redux selector function like useSelector(state => state.x)? Should you wrap every function in useCallback? With classes we had arrow methods that ran once, while useCallback will be run every time the function component is run. We have to continuously check that function references are stable, if it matters, and if we care enough to bloat the function with various memo calls.

Now I'm not at all saying that class components are better. Hooks are mostly easier to work with. But there's no doubt that function components has me using too much brain power and lines of code on memoization. I like the new features the react team are working on, but I hope they'll eventually do something about the stable function reference problem as well.