Kind of like a Clif's notes for the post.

Tells you either what content you'll find in the article, or shows everything that might be interesting, so you can save time by not clicking it and reading the post.

I could use a Discussion post here on SN instead, and put all that up in the Text field for that post, but then the "Twitter Card" image for the post has just that text, and not the Twitter card for the post that was linked.

Sorry if it seems odd or ugly to you. Search engine crawlers seem to like it though.