A content management system is used to maintain the navigation, images, documents and text on your website. Therefore you do not need to contact your web designer every time you need an update. I only create web sites maintained by a CMS.
When are they used?
- When you design a site for the first time
- When you re-design a site
- If want an existing site maintained by a CMS (you would be better off re-designing a site if this is the case because the whole site has to be re-programmed anyway)
I regularly use two open-source content management systems and neither require licenses or have any ongoing fees: