The canonical tag by itself is a tool for Google and other search engines to know where the "primary" page for any content resides. A canonical tag is generally used to avoid duplicate content issues in case there are multiple pages with similar content or multiple paths to the same page.
Canonical tags are important if you use comparison shopping engines and those sites have links back to your Yahoo store (which most do). The canonical tells Google when they see a page, the url in the canonical tag is the main one for that content. If you have a page at say abc.html and you give shopping.com a url with tracking (abc.html?tracking). It's possible to see the link and end up at (abc.html?tracking) and think it's a duplicate page to abc.html . The canonical will point to abc.html and tell google that even if it hits abc.html?tracking , the main page is abc.html and so the ?tracking one isn't a duplicate page.
This also can happen - and is even more likely - if a user clicks through a shopping link, gets the '?tracking' url and then posts it on a blog, site, etc... Really anything that adds parameters to the url can cause Google to think you have duplicate content without the canonical tag. Canonical provides security that Google won't see duplicate data.
If you don't have a Google Products feed or feeds to other comparison shopping engines, you should and we can help. Go to http://www.feedwizards.com and we can get your data feed established ASAP so you don't miss out on the free traffic it provides.
Order now and maximize your SEO by greatly reducing or eliminating duplicate content issues caused by multiple similar pages or multiple paths to your product pages.
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