Videos can enliven a presentation. They can be used to illustrate something that would be hard or impossible to recreate on stage or with static slides. So there's nothing wrong with showing a video, presuming it is short.
But how long is "short"? Think back to the last time you watched a video in someone's presentation. 30 seconds are fine. One minute, however, can already feel long. Get to 3 minutes and all you want is for the video to end.
Why is that so? Why can't we bear to watch a 5-minute video but sit through entire movies which are 90 minutes or longer?