This feature mitigates bounce tracking on the web. It works by deleting state from sites that access storage during a redirect that the user has never directly interacted with. See the specification for more details.
Redirects can be used to implement cross-site tracking of users. In addition, redirects can be used to simulate third-party cookies even when the user has chosen to block third-party cookies. The primary goal of this effort is to mitigate these privacy issues.
Docs: https://developer.chrome.com/docs/privacy-sandbox/bounce-tracking-mitigations https://developer.chrome.com/blog/bounce-tracking-mitigations-dev-trial
Samples: https://bounce-tracking-demo.glitch.me
Explainers: https://github.com/privacycg/nav-tracking-mitigations/blob/main/bounce-tracking-explainer.md