Consider that... all sorts of service calls can be used - specific posts, forms, browsing results, profile cards, join form, etc.
Then think of how it could be used while building pages in Studio - not just replying on available builder blocks and settings, but simply creating an empty page with custom block and throwing together any combination of these macros, text, layout, etc. Say, a page like a footer-less, header-less login page with centred login form can be made in a minute and no need for special settings in the builder!
Or, say, adding a few cards of team members profile into the About page, regardless of whether they share specific membership, featured status, or anything that we may have built a block for. Just add any IDs and it will render cards.
Or, say, a Documentaton page, linking to various specific posts, discussions, articles, not with static text links that you have to update if anything changes but with embedded cards that update if posts are edited.
If we take it far enough you could build entirely custom pages with unique combinations of functional elements.
Some of these macros could be available for site members, not just admins - so they could serve as internal embeds, "attached" posts/media/etc. Say, I post some videos to Videos module, and then create a blog post with a few of those video cards inserted within my post.
Or, I could write an announcement, and encourage people to create new discussions when they have question, and actually embed a "Create Discussion" form into my post.