If you are in the business of building/maintaining a company's website or building web properties for an agency, you can and should be using mobile first strategies. Why? Because it is of value to your end product. You will end up with a website that is used by most of the people on all the devices and browsers possible.
This book is targeted at both beginner and intermediate developers as well as designers. It is also intended to be for those in business and management who want to gain a deeper understanding of what is possible (and, by extension, what may not be practical) with modern tools and strategies on the web. The code examples in this book, when used step-by-step, should help anyone with even basic development skills to get a deeper understanding of what is possible as well as how it is possible. Of course I love building things and I do it every day, but for those of us who also have to strategize and educate clients and coworkers, having procedural knowledge of how to make a mobile first website is qualitatively better than only having the knowledge of theory and concepts.