You will use the canonical field when posting an article from another Base site (cross-post).
To cross post, you will copy & paste the article from site #1, to site #2 (There isn't an automated way to republish.)
When the article is republished on site #2, paste the URL of the article from site #1 (the “canonical source”) into the canonical URL field. That alerts Google what the source of the article is, and prevents both sites from being penalized.
