Why it matters
Every renamed or removed page without a redirect becomes a dead end: visitors hit errors, and years of link equity evaporate. Redesigns that skip redirect planning are the classic way sites lose half their search traffic overnight.
How it works
Rules map old paths to new: anyone requesting the old address lands on the new one, and engines eventually update their index while crediting the new URL. Permanent (301) signals "moved for good"; temporary (302) preserves nothing long-term: use it only when you mean it.
What to do about it
Before any URL changes or relaunch, export the current URLs, decide each one's destination, and test the map after launch. It's a spreadsheet's worth of work protecting years of accumulated traffic.
