When is it recommended to use a self referencing rel "canonical"?

[SEO_Promenade]

In what type of a situation is it the best type of practice to use a self referencing rel "canonical" tag?

Are there particular practices to be cautious of when using a self referencing  rel "canonical" tag?

I see this practice used mainly with larger websites but I can't find any information that really explains when is a good time to make use of this practice for SEO purposes.

Appreciate all feedback.

Thank you in advance.

[JaneCopland]

As others have said above, combating scrapers is a big reason, but you're relying on lazy scrapers not removing the tags.

Another reason is to prevent rogue content management systems from attaching unnecessary query strings to URLs, creating pages that can end up loading infinite times under different URLs. A canonical tag in the source file would mean that any number of duplicate pages point back to the original. The same reason goes for sites that have issues with redirecting www / non-www URLs to the correct version, or who deal with the same problem regarding secure / insecure URLs. In all these cases, the canonical tag is a bandaid, not a cure - it would be better to fix the underlying problem of the rogue CMS, incorrect redirection, etc. but the canonical tag (self-referencing) is there if you need it.

Google doesn't seem to have an issue with it, but if you're at all concerned about the other engines, use with care.

[AlanMosley]

People do it to stop scarpers, but if your going to write screen scraper it would not be hard to remove canonical tags as well. so I don't think much of the idea.

Bing recommends that you do not use self ref canonicals tags. It could be that a self ref canonical tag may be followed as is alluded to by Bing, meaning that lose a bit of link juice thought the redirect.

[VWE]

You may want to just use it on every page.

One good argument for using a self-referencing rel=canonical on every page is to combat scrapers. If they grab the entire code, including the rel=canonical, they are essentially telling the bots that your page is the original, and they'll be much less likely to outrank you for your own content.

Larger sites tend to generate the rel=canonicals automatically for every page, and give you the option to customize it where necessary.

[OlegKorneitchouk]

What do you mean?

Like on site.com/pagea.htm there is a canonical set to site.com/pagea.htm? No harm in that. You should have a canonical URL whenever you want only one specific version of a URL.