Does it do harm if you add a rel="canonical" tag on a page that doesn't need it?

[jaychow]

If a page is clearly unique and there is obviously no canonical tag needed, does it hurt anything if one has been added?

[MattAntonino]

In my opinion, you want the juice for each article to stay with each article.  I wouldn't redirect all your article juice back to the main /blog page.  For me, each unique page (and article) gets its own canonical link and one line = one set of information.  Article about oranges, article about apples, both canonical links.  You should only get juice from same or similar pages, such as

yoursite.com/

yoursite.com/index.php

www.yoursite.com/index.php

www.yoursite.com/

But not

yoursite.com/oranges/

[jaychow]

hey matt, thanks for the response.  let me ask you this.  i have a blog page with a bunch of snippets, that when clicked, lead to the full articles, (each have their own custom page/url).  if i want all the juice to go to the main blog page i don't want to have canonical tags on each individual post page, right?

[TakeshiYoung]

Agreed. You page can sometimes end up with query parameters as well when people link to your site, and having the canonical in place will help you avoid having duplicate content.

[MattAntonino]

It shouldn't hurt you if it doesn't need it but assuming you have www and non-www, wouldn't that part of the canonical always help anyways?  By default, you would have

http://www.yoursite.com/notagneeded

http://yoursite.com/notagneeded

and if you're on most common CMSs,

http://www.yoursite.com/notagneeded/index.php or index.html or index.asp

It would actually be pretty rare to have a page with absolutely no use for rel=canonical but I don't see why it would hurt at all.