A performance budget is just a number you agree not to exceed — total JS shipped, or a Lighthouse score threshold — checked in CI, not just eyeballed occasionally.
Pick metrics tied to what users feel
Largest Contentful Paint and Interaction to Next Paint track much closer to "does this feel fast" than a raw Lighthouse score does.
Automate the check, don't rely on memory
A budget that isn't enforced in CI quietly erodes the first time someone's in a hurry.