CMS (Content Management System) are basic software structures that allow the developer to start from a solid base already created.
The use of a CMS in web design is now indispensable because it saves a lot of time, and therefore lower costs for the customer.
The basic function of a CMS, or that of “content management”, remains the main strength of these structures: a website developed with a CMS allows the customer to easily create and manage new content without programming knowledge and therefore interventions external (even if for the optimization of images and videos and the writing of the texts it would be better to contact professionals).
This is very useful when creating a blog or e-commerce, for example, which needs to be updated frequently.
The most famous free platform on the market is WordPress, which allows a high customization of the style and functionality both by modifying the source code of the theme used, and through themes and plugins that do not need to put your hand to the code. This is why WordPress is used as the basis for a huge number of websites in the world. The WordPress system also guarantees excellent modularity, allowing you to update the plugins or even the core without changing the theme developed.
Internally developed CMS are used in many agencies to have greater control over development and security. This is useful for large agencies with a lot of staff and a particular workflow, for small businesses I find it more profitable and safer to learn how to manage a system tested and maintained by competent people like WordPress. Another advantage of the widely used CMS is the large community of people who develop and / or use them, who can help the developer to solve problems or doubts faster.
Unless you have very high performance requirements, WordPress is an excellent CMS and reinventing the wheel often makes no sense.
The most used CMS are usually Open Source, that is, the source code is free and editable. This is very important because if you are able to intervene on the code you can get extreme customization.