If the site has no duplicate pages, whether relevant tag rel=canonical?

Welcome

Thought about using rel=canonical — to prescribe or not. On the website are no duplicates, but I read once that someone can add in the "addurilku" page with some parameters (sometimes notice these pages in PS). Also sometimes some people copy the HTMl pages, changing only the names. Will help in any way add rel=canonical, what would you advise — to be or not to be?