Everybody knows that Google does not like "pages not found" errors (404 error), it may be detrimental to the SEO of your Drupal website, we will try to avoid it easily and effectively.
When we use the Path Auto module most of us use the token
[node:title] combined with others to create a friendly URL for each node. In the configuration of the module can select the option "Automatically create redirects When URL aliases are changed." The Redirect Module automatically generate permanent redirects (301) to the new aliases. This way we avoid page not found errors and lose no referral traffic.
Download Redirect Module