In order to get a consistent looking website, many designers use a common layout or master page. That’s good, but in practice we often need to add some other items to the layout too. Say, for example, we have a different style sheet or Javascript files for many of our body pages. We can achieve that using Sections.
CSS Frameworks undoubtedly help in providing a quick and pleasantly aesthetic look to your product and can give considerable help in providing the base HTML, CSS and JS required. For a developer like me, CSS Frameworks contribute many of the modern standards and techniques which I may lack as a non-designer. Creating a good responsive design from scratch is not a trivial exercise so a good CSS Framework can give you a great base to start from.