It's so annoying to me that so many CMS's and static site generators start out with the assumption of 1 big rich text / markdown "body" for content and treat everything else on the page as miscellaneous stuff (meta-fields, yaml front-matter, etc).
Is it for meta information about a post? Are those fields injected into a post somehow? How are those fields used? (I'm ignorant of CMSs)
Obviously rarely the case, but worth having the conversation.
The user facing html templates have variables that map back to those fields. So, all the expression of HTML, but with the actual data in fields.
Handy for things like addresses. You can render a map or just text, or both. The fact that it's structured data would allow for proximity searching. Where each "post" is say, a restaurant location.
Similar for things like tags, so that you have built in taxonomy. Separate spaces for tags too, so that you could have a topic taxonomy as well as a completely separate taxonomy that doesn't pollute that space. Like an author taxonomy or similar.
Others allow content relationships, where videos are their own object, set not to be published alone, but embeddable into, say posts.