Magento 2 performance is not a cosmetic issue. It affects SEO visibility, paid traffic economics, product discovery, and checkout completion.
Start by measuring Core Web Vitals, cache behavior, server response time, JavaScript execution, image delivery, and extension overhead. The fastest wins often come from removing unused scripts, tuning full-page cache, cleaning theme output, and improving media delivery.
A serious optimization project should also review PHP-FPM, MySQL, Redis, Varnish, CDN behavior, and deployment practices so the store remains fast after changes.