Having duplicate or similar content on various pages can cause issues with ‘unwanted behavior’ from Google.
If you have duplicate versions of the same page, Google will classify one of the pages as the main version or original, and run with that. Unless of course you set one URL as the canonical version.
If you don’t explicitly tell Google which URL is canonical, Google will make the choice for you, or might consider them both of equal weight, which might lead to unwanted behavior
If you do not choose one URL as the canonical version, then Google will themselves:
Choose one URL as the canonical version and crawl that, and all other URLs will be considered duplicate URLs and crawled less often.
This underlines the importance of the correct use of canonical URLs, as we also covered in this post.