Building websites that look beautiful and function flawlessly across different devices is a must for every serious front-end web developer.
Failure to optimize your website for different devices means your website will only look good on some and not all screens, and that's a bad practice. The effect would be low return visitors, with many first time visitors landing as soon as they realize that your website neither looks good nor functions smoothly.
There is a way out of that mire, though, and that's the whole idea of this chapter of our CSS course.