i *believe* in the pre-hybrid era the point of these things was to differentiate yourself amongst a parade of other people giving 30s previews in a "fast-forward" session, and so things like humor or being memorable were valuable. I only went to a couple conferences in that era, so i don't really know

In this era Ive seen them used in two ways
1. played without sound on TVs in common areas of the in-person part of a conference
2. as bumper material in live-streams before/after paper sessions