Permanent redirects are the strongest signal an origin server can send that a URL has moved for good. Both 301 and 308 mean the same thing at the semantic level: stop asking about the old address. The practical difference is how they treat the HTTP method. A 301 historically allowed clients to downgrade `POST` to `GET` when following, because that is what early browsers did; 308 preserves the original method and body, which matters when redirecting API endpoints that receive form submissions. Search engines consolidate signals (including backlinks and ranking weight) onto the target URL within a few crawl cycles. Browsers and CDNs aggressively cache permanent redirects — sometimes to the point where reverting requires users to clear their local cache — so permanent redirects are a commitment. URL shorteners rarely use permanent redirects by default because campaign destinations may legitimately change after launch; they reserve 301/308 for links flagged as immutable. Site operators use them heavily when retiring content, consolidating duplicate URLs onto a canonical, or moving whole hostnames during rebrands.