When memo actually helps

memo skips a re-render when props are shallow-equal. It costs a comparison on every render, so applying it everywhere makes things slower, not faster.

What this lesson covers

• Apply memo to expensive subtrees with stable props
• Understand shallow comparison and why objects defeat it
• Recognise when restructuring beats memoising

This lesson sits in Rendering Optimization, part of React Performance Engineering. It assumes what came before it and leads directly into the next lesson in the module.