Content management systems are usually software that manages and controls content, allowing groups of people to create, edit, and share content. Content management systems are not only used for websites, rather they are normally used for all forms of digital media. Along with creating and editing content, content management systems are a very good tool to organize and manage content.
Building a website using a content management system and building a website using HTML/CSS would be very different experiences. By using a content management system you would be able to collaborate on your project, and you would ultimately be able to customize your website much easier. Along with this, however, you may not be able to customize your website as much or as specific as you could by using HTML. So a drawback of using a content management system is that you would have less customization, while a drawback of HTML would be that it would take much more time and effort. The current best practice to creating a website would probably be CMS, but it is up to the user. As time goes on HTML basically stays the same, while CMS advances and continues to give the user more freedom, customization, and accessibility.
CMS impacts the web design industry, as it makes it so much easier for anyone to create a website however they like, with easy steps and freedom. This could potentially take jobs away from web developers of HTML or CSS, but overall it will just split into two groups of people. Along with that, HTML developers have much more experience and knowledge in the area, so they will also be suited to create CMS websites if needed.
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