Ok, React.memo HOC mimics for a "function component" what extending React.PureComponent would do for a "class component".

If some rerendering was triggered by some parent component, pure components don’t rerender if its props haven’t changed. Ok

But i can’t understand when i should not use React.memo for function components. In my mind, it appears to be always the best solution, in a way that should be the default behavior of React components. But it isn’t. What am i not understanding of this? In which example we should not use React.memo or rely on pure components?

And if my React Component shouldn't be Pure but I made it so, what are the disadvantages?