I tend to write summaries for all my hubs. Due to the fact that if it is to display in a search engine, even as a description or a synopsis, it probably could give the viewer a higher chance of actually clicking through to the link. If they are able to search, and read on the immediate page that they are viewing, the details regarding what your link is about, the odd's are greater that they will navigate to your page. At least this is what I would think. Because even personally, I tend to search for subjects and have a greater likelihood to browse to pages that include accurate descriptions rather than unappealing captions or on the other hand, nothing at all.