What does "Load link previews" do?
It fetches thumbnails for links in your conversation, so YouTube videos and songs print as little preview cards.
Conversations are full of links: songs, videos, articles. Click "Load link previews" at the top of the editor and we fetch a thumbnail and title for each link, so it prints as a small preview card instead of a bare URL.
You can also generate a preview for a single message: hover it and choose "Generate link preview" from the toolbar.