Hmm, it’s context specific though isn’t it? Grouping is an important way of identifying if a series of content is related to one another. The boxes on Facebook news feeds for example group the post content, the likes and the comments together, visually indicating they are related — much like the newspaper horizontal rule does in traditional print media.
On the Google search results page, grouping is indicated by the link colour — boxes don’t add anything to that visual division .
I notice in your example, you use a hr as a divider instead of a box — in this context that could work — it just depends on preference and context. If that example had more complex content (ie, grouped comments or some such), then I’d want the contrast of a border-box.