I am a little bit confused about this tag. I have read about this on Matt Cutts blog and have watched the video above. He gives the example of an online shop where a page with a product description can show up several times. In his example it's a website for a certain gummy candy called swedish fish.
The customer can access the product page with various links:
The simple product page:
The product page in the category: gummy candy
I'll come up with a third:
The product page in the category: gelatine free sweets
And a forth:
The product page in the category: salty sweets
Note, that in the example Matt Cutts gives, the category and product name is displayed in big bold letters, so the visitor can immediately see two informations:
1. In which category he is on the website
2. Which products are displayed.
Now Matt Cutts happily tells us: We can resolve this duplicate content issue by picking one of those product pages and making it our "canonical page" with the new "canonical tag".
So here is my problem: I do not think those pages have a duplicate content issue. I do believe that those four pages are entirely different and for some users the essential information lies in the 1 percent of information that differs in those four examples and that this information for me as a shop owner can decide if I make the sale or not.
What if a user searches for: "Gelatine free swedish sweets"?
Will my product page even show up now in the search results if I use No 1 as my canonical URL?
And even if it does - won't my potential customer be confused if he specifically searched for "gelatine free swedish fish" and this important information does not show up in a prominent place because I directed him to my "canonical URL". What about the user who wanted "swedish salty sweets". What about the user who wants "swedish gummy candy".
What if I made the URL "salty sweets" my canonical. Won't a visitor be confused if he does a search for "gelatine free sweets" and then ends up with "salty sweets"? That wasn't the information he was looking for.
When I understand the implications of the canonical tag correctly I might loose 75% of my sales on swedish fish if I use this tag.
I checked my own online shop. Tried searches like
product_type + part of product name
brand + part of product name
For both searches Google showed me another URL. However the correct product at its correct location in my website - for the specific search. One in the "brand category" one in the "product type category" How it should be. Like a visitor would expect it.
I would be nuts to implement this tag. It's fixing something that is not broken. Or did Matt Cutts only use a bad example?