In reply to Mike Bates.

Like most things, it depends. For the most part, users do not need to create child themes to overwrite things from the parent theme.

When using the site editor, you are essentially creating a child of the active theme. So, the hierarchy basically goes like this:

User templates and styles
Child theme (if active)
Parent theme

If you are overwriting or creating custom templates, you can do this straight from the editor. If you want to change global styles, this is also possible via the editor. These will take precedence over the active theme.

With that said, there are still some things that are simply not possible from the site editor. If you have a lot of custom CSS that is not configurable via the global styles panel, you might need to create a child theme. With WordPress 5.9 (should be fixed in 6.0), it is not possible to create a full range of custom templates. For example, if you want to separate your "Business" category template, there's no way of creating a taxonomy-category-business.html template via the editor yet. So, you'd have to add that via a child theme.

There are many small things that could require creating a child theme. But, in general, you shouldn't need to.

If you're just concerned about protecting customizations from parent theme updates, what you save via the site editor will still be in place.