Duplicate content has been an important topic for webmasters for years. It should be absolutely no secret by now that duplicate content is generally dangerous to a site and usually offers no value, but there are occasional reasons for duplicate content to exist.
Of course, there are very real risks with hosting a significant amount of duplicate content, but often the fear is larger than the actual risk of penalties – so long as you aren’t taking advantage and purposely posting excessive duplicate content.
Google’s John Mueller puts the risk of using duplicate content in the best context,. According to John, there are two real issues with duplicate content.
The first issue is that Google’s algorithms typically automatically choose one URL to show for specific content in search, and sometimes you don’t get to choose. The only way you can effectively let Google know your preference is by using redirects or canonical tags, and that isn’t foolproof.
Secondly, if you are hosted a ton of duplicate content it can actually make the process of crawling to overwhelming for the server, which will slow new content from being noticed as quickly as it should be.
Still, John said that in most cases, “reasonable amounts of duplication […] with a strong server” is not a huge problem, as “most users won’t notice the choice of URL and crawling can still be sufficient.”