ZydoSEO - 2:38 pm on Jan 22, 2013 (gmt 0)
While "most of the time" Google may be able to figure out that /page.html and /page.html?ref=sidebar are, in fact, the same page, why on earth would you even want them to have to? Why even take the chance? And Google isn't the only engine out there. While Google may be able to figure it out, other engines might not.
I constantly hear people here say, "Ah... It's not an issue. Google can figure it out and won't treat as duplicate." Google "tries" to determine which of the URLs is the canonical and give it credit for all of the other non-canonical pages' links, but they don't always get it right. Be explicit. Using a single canonical URL for all of your links on your site is so easy. With the exception of huge ecomm sites where there are often needs for query string parameters for sorts, filters, categorys, sub-categories, etc. using a single canonical URL on your site for every page is usually a no brainer.
Query string parameters in general are a bad idea because each value of a parameter as well as the order of the parameters create new URLs, even though ALL such URLs may render the same content. The same page could have literally millions of URLs in some cases when you consider all of the combinations and permutations parameters and values.
Using query string parameters for tracking, especially for internal tracking of where people on clicking on your own site, is just ludicrous. 99% of those that implement such internal tracking "might" look at it once, and then rarely if ever look at the results again.
The really bad thing about exposing non-canonical links like /page.html?ref=sidebar on your own site is that the way most people create links to your site is by browsing to a page on your site, copying the URL from the browser address bar, and pasting it into a link. Depending on which link they clicked on (top nav, left nav, footer, etc) to arrive at a page to which they want to link, they will get a different URL. So you're perpetuating having other sites link to your URLs with a variety of non-canonical URLs.