Ephemeral content is made to expire, and the expiry is the point. A stories-format post, a today-only offer, a countdown that ends: scarcity creates a reason to look now rather than later.
On screens it fits naturally, because a physical location already supplies the "here" and the expiry supplies the "now". A lunch offer that visibly runs out at two o'clock outperforms the same offer running all day, for the same production cost.
The caveat is that expiry has to be enforced by the system, not by a person remembering. The failure is universal and embarrassing: a Christmas promotion still playing in February, or a countdown at zero. Every time-bound asset needs an end date set at upload and a defined fallback for what plays after it.
The related discipline is deciding what the screen shows when nothing is scheduled. Networks without a defined default eventually show a stale campaign forever, because nothing forced a decision when the campaign ended.