Performance work usually gets scoped as a checklist item at the end of a project. That is exactly why it rarely holds up after launch.
Performance is a budget, not a task
Teams that treat page-weight and load-time as a fixed budget — checked on every pull request — ship faster sites than teams that run a single audit before launch.
What we check on every build
Image weight, third-party script count, and render-blocking resources are the three levers that move Core Web Vitals scores the most in our experience.