Example blog posts and categories:

My blog posts have a reference to several categories.

This makes it possible to display all categories assigned to a specific blog post in a collection list.

It would be helpful if this also worked the other way around, so that you could display all blog posts that are assigned to a specific category.

This is actually possible in any normal, reference-based database.

For example, if I have the list of categories and use it as a filter on my blog page, all categories are displayed, even those to which no blogpost is assigned.

With the inversion, it would be possible to filter out only those categories that actually have a post assigned to them.