If you run a website of any significant size, odds are you utilize some form of content management system (CMS). WordPress, Drupal, or the like.
And, if you don’t use such a system, you probably employ rather extensive use of some form of server-side, scripted, page generation. PHP, ASP, Ruby… the list goes on and on.
There are many scenarios where such a system makes a great deal of sense. But I’m here to tell you, right now, that it is highly unlikely that you actually need them… at least for the majority of your page.