Categories and tags are the two default WordPress taxonomies used to organise content, with categories serving as broad, mandatory groupings (like topics in a library) and tags providing specific, optional keywords for granular details. Categories are hierarchical (parent/child), while tags are not.

In practice individual sites will have their own guidelines for how to use them.

Personally, I always assign a post to just one category, and add tags as required. But the perennial problem remains - is a map of the Roman empire in category 'Map' tagged with 'Roman Empire', or in category 'Roman Empire' tagged with 'Map?.

This video makes some interesting points:

Now it's clear that I don't need full site editing and only need the block editor for the Home and Blog pages, convert all other pages and posts to the classic editor.

I'm surprised this isn't part of WP core. There are a few plugins which address the problem, at least one of which admits to being susceptible to being bypassed by a knowledgeable hacker. It ought to be possible to see how strong a user's password is from the dashboard.