How can URL parameters, like session IDs or tracking IDs, cause duplicate content? When user and/or tracking information is stored through URL parameters, duplicate content can arise because the same page is accessible through numerous URLs.
Duplicate content. There's just something about it. Let's put this to bed once and for all, folks: There's no such thing as a "duplicate content penalty." At least, not in the way most people mean when they say that.
Duplicate content generally refers to substantive blocks of content within or across domains that either completely match other content or are appreciably similar. Mostly, this is not deceptive in origin. Examples of non-malicious duplicate content could include: