Nofollow X-Robots-Tag Wouldn’t Stop Google Following a Redirect
A nofollow X-Robots-Tag wouldn’t stop Google from following a server-side redirect, as Google wouldn’t even look at the content of the page so there would be no links to follow anyway.
Guest Post Links Should Be Nofollowed
John recommends having rel=nofollow on the links in guest posts.
Nofollow Obsolete When Noindex Already Present
When a page is noindexed, not only will it be removed from the index but also over time all of the links associated with the page will be removed from the link graph so nofollow is made obsolete.
Use Nofollow to Stop Googlebot Crawling Too Far
Google recommends using internal nofollow links to stop Googlebot crawling too far in one direction e.g. endless calendar links, faceted navigation and pagination.
Googlebot Crawls URLs in JavaScript Code But Treats Them as Nofollow
Googlebot crawls urls found in JavaScript code and automatically nofollows them. If the JavaScript modifies the HTML, then Google will respect a nofollow attribute.
Unnatural Links to External Sites Might Cause All Links to be Ignored
Unnatural links to external sites, such as paid links or links within user-generated content may cause Google to lose trust in all the links from a site, so they should be nofollowed.
No limits to the Number of Nofollowed External Links on a Page
Google doesn�۪t have a limit for the number of nofollowed external links on a page.
Google Passes Signals Normally for Links with rel="noopener noreferrer"
Following a recent WordPress update, rel="noopener noreferrer" attributes have been added to links opening in a new tab. Google ignores these attributes and passes all signals normally for these links as long they don�۪t have a nofollow.
Google Might Nofollow Links in Widgets and Apply a Manual Penalty to the Target Site
If Google detects a significant number of links within a widget, it will nofollow them, and may apply a manual action penalty to the site where the links point to.