Disavow Backlinks on New and Migrating Domains
If you migrate a site to a new domain which has unnatural backlinks, you should disavow the unnatural links on the new domain as well.
Use Disallow to Improve Crawling Efficiency
John recommends against robots.txt, because it prevents Google consolidating authority signals, but then says there are occassions when crawling efficiency is more important.
Submit Sitemaps with Changed URLs
If you change many URLs, you should submit a sitemap with the old URLs to Google which will help them pick up the redirects to the new URLs. Webmaster tools will report errors with the sitemap, because it only contains redirecting URLs, but this is fine.
301 Redirects Pass Full PageRank on a Site Level but Not per URL
If you redirect a full domain, e.g. www to non-www, or http to https, the full authority will be passed over, but individual 301 redirects do not pass the full authority.
Every Step in a Redirect Loses Some PageRank
With redirect chains, some additional authority is lost for each redirect in the chains, so you should minimise them, but the amount is small. Google recommends getting links updated to point directly to the new URL.
302s Will Eventually Be Interpreted as 301s
After a long time, a 302 may be interpreted as a 301.
Canonicalised Pages Stay in Google’s Index
Canonicalised pages may remain showing as indexed for site: searches depending on the ‘site structure’. They are no considered as hard as a redirect, and the page can still surface for unique content. Canonical URLs are not crawled immediately, like a redirect would be. John suggests that if you have a large number of incorrect canonical tags, such as many pages canonicalising to a single page, they might ignore all canonical tags across the site. Google makes a clear recommendation that cleaning up broken canonical tags is a good idea.
Redirecting URLs Do Lose Some PageRank
Changing URLs and using redirects does result in a small loss of PageRank. Keeping original URLs is still better if possible. This is also why Google recommend updating backlinks.