The canonical tag helps webmaster to show Google the preferred URL of a web page. Some people only use the canonical tag when there are duplicate pages that show the same or similar content.
Other people include a self-referencing canonical tags on all pages, even if there is only one page with that content. In a webmaster hangout, Google’s John Mueller said that they recommend self-referential canonical tags:
“I recommend doing this self-referential canonical because it really makes it clear to us which page you want to have indexed, or what the URL should be when it is indexed.
Even if you have one page, sometimes there’s different variations of the URL that can pull that page up. For example, with parameters in the end, perhaps with upper lower case or www and non-www. All of these things can be cleaned up with a rel canonical tag.
You can view the statement of John Mueller here:
Check the canonical tags on your web pages
A self-referencing canonical tag can also help when someone scrapes your content. If the scraper also publishes the unchanged page with the canonical tag, Google will be able to identify the original page.
The website audit tool in SEOprofiler checks the canonical tags on your web pages (as well as many other things). Create a free SEOprofiler account now and check your website: