You probably thought I was going to say responsively (we'll get to that).
Web content management systems come in all shapes and sizes and with all kinds of functionality. Some tools are used as a CMS without initially being designed as one. Sometimes a CMS will have additional features that can't be categorized into managing content. Regardless of what you use, it's important to manage your content properly.
Arguably the primary purpose of a web CMS is to easily manage the content on your website. The CMS should provide you intuitive ways to change copy or upload images without having to do all the work of formatting it for a browser. Ideally, after you've entered unformatted content, the proper web formatting and design will be applied programmatically as it is published to the site.
Separation of Design and Content
This is where we need to act responsibly. Too often we try to use the CMS as a content formatter rather than just a content manager. But if we try to format our content before we store it we lose the flexibility that unformatted content has. Allow the formatting to be added programmatically and the possibilities are endless.
Welcome to the Responsive Era
Never before has clean unformatted content been so valuable!
Since the introduction of responsive design, the format fits the environment. Content needs to be flexible to fit any device. If your CMS has the power to pre-format your content you are potentially removing the power CSS has to be responsive.
Many CMS tools give us the ability to format text in any size or use tables to create columns. This type of flexibility can be desirable to have, but requires a deeper look to see how the content is being stored. If the style decisions have been stored along with the content then we've lost our ability to adapt to the user. Look for a CMS that stores content in clean organized pieces of plain text and HTML.