Too Long; Didn't Read
You're left with a handful of HTML files, images, and one or more CSS and JavaScript files. Inevitably, you’re going to want to change something with the site, and then what? Are you going to go all the way through the design process again? A more sustainable approach is to take the static HTML content you were given and templatize it! Make it easier for you to work with — to make changes and to create new pages — when the need arises.