One of the adverse side-effects of modern web applications (websites) is the increased complexity of maintenance. Consumers are content-oriented; each consumer is on a daily quest to find the most relevant content available. Consumers find this information from the web, particularly from sites like Instagram, Twitter, and Reddit. If you want a relevant website and company, you must be providing content on a recurring basis to help drive website traffic and company growth.
The best websites in the world for their particular sector of the internet are the best because of their ability to post relevant content seemingly on the fly. This is where a Content Management System (CMS) comes into play. Often, content creators are not technically oriented, and if they are, they are often not web development oriented. Even for this blog, I am typing into a markdown text editor, likely out of the scope or desire of most content creators. As a web developer, this is the easiest and cheapest way to accomplish my purposes. However, if I am commissioned to build websites for non-technical clients, I still need a way for them to easily add content.
Content Management Systems are graphical user interfaces for adding and manipulating content on a website without having to code. There are free, open-source options as well as paid, feature-rich options. If I have a website created by a developer who included a CMS in the website, I can go into the CMS interface, click on "add blog post"-or something similar-and type into a Microsoft Word-esque editor. That content will be processed by the CMS and converted to the markdown language for processing by the website.
If you have a website of more than a handful of administrators, a CMS is an absolute necessity to avoid falling into the website graveyard where the irrelevant, not-visited websites reside.