Sometimes you want to allow your users to move content out of the way. I makes them feel powerful, engaged and can allow them to focus on the (important) remaining content.
The collapsible body — the element that is exposed after the click — can contain all sorts of (secondary) content, including links to even further explore the subject.
The IDs of the dismissable and trigger will need to be updated if you have more than 1 dismissable on a page.