Every deleted page, changed slug and site restructure breaks URLs that Google and other sites already point at. A redirect is how the value of the old URL survives at the new one. Done right, moves cost almost nothing; done wrong, rankings quietly evaporate and nobody connects the cause.
1. Use the right status code
A 301 (permanent) transfers ranking signals — it is the correct choice for almost everything: renamed slugs, retired pages, domain moves, http→https. A 302 (temporary) tells Google to keep the old URL indexed, right for genuinely temporary situations only. When in doubt, 301.
2. Map old URLs to their closest match
The redirect target should satisfy the same intent as the original. Old product → its replacement or its category; retired service page → the nearest current service; merged posts → the surviving post. Redirecting a batch of dead URLs to the homepage is the classic mistake — Google treats irrelevant redirects as soft-404s and passes nothing. Build the map in a spreadsheet before touching anything: one row per old URL, its new destination beside it.
3. Implement cleanly
A redirect plugin (Redirection, or your SEO plugin’s module) is fine for tens of rules and gives you logging. For hundreds of rules or a full domain move, server-level rules (.htaccess or nginx config) run before WordPress loads and cost nothing per request. Whichever you use, keep the map file as documentation — the next redesign will need it.
4. Kill chains and loops
Redirects accumulate: A→B from an old migration, then B→C from a new one, and now every visit hops twice. Each hop wastes crawl budget, slows users, and can shed a little signal. Periodically crawl your redirects (Screaming Frog does this well) and flatten every chain so the oldest URL points directly at the final destination. Loops — A→B→A — take pages down entirely and need fixing the day they appear.
5. Verify after any big change
After a restructure, test your top 50 old URLs by hand or crawler: each should answer with a single 301 to a sensible page. Then watch Search Console’s 404 report for a few weeks — every unexpected 404 with real traffic gets a rule added to the map. This is exactly the process behind a redesign that keeps its rankings.