What problem does this address?

This issue is copied from trac, https://core.trac.wordpress.org/ticket/59811, please read the full conversation there.

Right now, in the pre-publish screen, we suggest users to add tags and categories to their post. I'd like to make a few changes to what we do there, and I'll explain why:

If no tags and no categories are selected, we could suggest adding either a tag or a category. But:
If a site doesn't have any tags, we shouldn't suggest adding tags.
If a site doesn't have any categories, we shouldn't suggest adding categories.
If this leads to not suggesting either, then that's fine.
Right now, we suggest adding tags and categories to every page. Every time someone creates a new tag that way, we create a new URL on the internet that needs to be crawled, when really that page might not be very useful at all.

In my ideal world, if a theme has no support for tags (many don't show tags on post pages), we shouldn't even have an interface for it. We might consider adding something like an add_theme_support feature for tags, where we default to it being on but allow themes to remove_theme_support for tag pages and then not show tags in the interface, or something similar to that extent.

And the reply from @mtias :

I like the idea that if the site doesn't have tags or categories in use at all we could avoid showing the corresponding suggestions UI. That seems like a practical step to look at.

More broadly, I think part of this falls in the same bucket of customizing the features that are relevant and reflecting that across the admin UI. If I have a site made just of pages, or have disabled comments, I shouldn't be bothered with that part of the interface, etc.

What is your proposed solution?

Do not show the tag and category suggestions in the pre-publish panel if there are no tags or categories on the site.