Use a 301 whenever a URL changes for good: migrating to HTTPS, changing a slug, merging two pages, moving to a new domain, or consolidating duplicates that a canonical tag can't fully resolve. Google transfers the vast majority of link equity through a 301, so rankings usually recover once the change is recrawled.
The key contrast is with a 302 redirect, which signals a temporary move and is treated differently. Using a 302 for a permanent change can leave the old URL indexed and slow the transfer of ranking signals.
Common pitfalls include redirect chains (A→B→C), redirect loops, and mapping every removed page to the homepage instead of the closest relevant page. A clean 1:1 mapping preserves the most value and avoids unnecessary 404 errors.
FAQ
Frequently asked questions
Google has stated that 301 redirects pass essentially all ranking signals, with no meaningful PageRank loss. In practice a correct 1:1 redirect preserves the great majority of the page's authority.