“Canonicalisation” means to indicate to Google that you want one URL to take authority over another URL that presents identical results.
This is done in instances where the 2 pages display exactly the same products. For example, if you have a brand that only sells coats, it isn't beneficial for Google to be crawling both the brand page and coats page for that brand. This becomes a conflict of interest as both pages will be using the same keywords to target traffic, resulting in identical or duplicate content appearing on multiple URLs.
The addition of this feature adds another menu to your admin where you can add and manage your canonical URLs.
Large scale duplication may dilute your ranking ability therefore, canonicalising your URLs will improve your SEO rankings and ensure traffic goes to the right place on your website.