As a front-end developer who have worked on many projects, I've seen a lot of content duplication in views.
Let's see an example:
For Spree applications, if we want to edit our Spree base layout, we should use Spree Deface to manipulate its contents since this is the recommended way. Another way is to copy, paste and update the layout content to make those little modification such adding some wrappers or titles. The real problem when using the second approach comes when you use those modified layouts as based for new section, then you realize you need another different layout with another small modification: you have to copy, paste and edit in order to generate another layout.