What’s duplicate content?
Duplicate content refers to the same or very similar content or blocks of content on multiple web pages. While there isn’t much you can do about your content being copied onto other websites, it’s very important that you avoid duplicate content between pages on your own website.
Some attempt to put duplicated (or very similar) content across multiple pages in order to try and win more traffic, but Google does track down and penalize this type of nefarious action by either only allowing the ranking of the site to suffer or completely removing the pages from their index. Duplicate content by chance doesn’t warrant any action from Google, but it can still have negative consequences on your rankings.
Negative Effects of Duplicate Content
Duplicate content can result in losses in both rankings and traffic to your site because it dilutes the visibility of each of the duplicates. Basically, you’re pitting your own website against itself and if you have two pages with the same topic or same content, you’re splitting the traffic between them and not helping yourself in the long run.
Search engines won’t know which version to include or exclude and which version to rank for query results.
The importance of not duplicating content on your website
For search engines, they don’t know which version to include/excluse from indices
They don’t know whether to direct the link metrics (anchor text, trust, authority, link equity, etc) to one page or keep it separated. They don’t know which version(s) to rank for query results.
It’s also bad for link equity. Link equity is the concept of external linking between pages on different sites giving the other site authority. If many websites of credible source and authority link back to you on a related topic, it acts like a vote of confidence and gives the site more authority. If you have multiple pages with the same content being linked back to, it once again muddles the quality of authority. Ten authoritative websites linking back to one page is better than ten authoritative websites linking back to three separate pages.
How to Avoid Duplicate Content
Some duplicate is actually the result of confusing URL parameters, so try to avoid adding URL parameters or making alternate versions of the page URL, or even having a page with both “www.” and without. For these situations, you need to decide which page is “correct” set up a page redirect. When all the variations of the page are ranked together, it helps with both the ranking and relevancy of the page.