The difference between a site you can edit and one you cannot.
Changing a price, adding a page or publishing a post happens in a browser. Without a CMS each of those is a code change and an invoice.
The words live in a database and the design is applied on top, so a redesign does not mean retyping the site.
More than one person can work on the site, with an editor who can publish and a contributor who cannot.
Forms, bookings, stores, multilingual content and SEO tools already exist for every mainstream CMS. You are rarely building from nothing.
Honest guidance, including when the answer is none of them.
The default for brochure sites, blogs and small stores. Largest plugin library, easiest to hire for, and the one most businesses should start with.
Stronger built-in user management and multilingual support than WordPress out of the box. A reasonable choice for membership sites and portals.
Built for complex content structures and strict permissions - large organisations, universities, government. More capable and more work.
If the site is one page that never changes, a CMS is machinery you will maintain for no benefit. A static page or a builder is cheaper to run and faster.
A CMS is database-driven, which makes it more sensitive to the server than a static site.
Every mainstream CMS drops support for old PHP, and running one on an unsupported version is a security problem rather than a performance one.
A CMS breaks most often during an update. A daily backup you can roll back from the control panel turns that into five minutes rather than a day.
Every page view is a database query unless something caches it. This is the single biggest difference between a CMS site that feels fast and one that does not.
On cheap shared hosting one compromised neighbour can affect you. Account isolation is what stops that, and it is worth asking about.
Plans for the CMS you have chosen.