Have you ever forgot your headphones, but needed to watch a video in a public, quiet setting? Have you watched TV while you were at the gym or at a restaurant? Captions benefit many people, as well as individuals with limited or no hearing.
Don't use videos without captioning. If you use software for automatic captioning, be sure it is right. Here is an example of a message that I received from Google Voice
Corey it's Elizabeth Bathtub incident So I'm a bathroom house. I get better be careful hon.
It should have been
There was a bathtub incident at my house. I better get back to working on it.
It is good for a laugh, but I had no idea what they meant.
Don't notify the user of an event using audio only. There are people that wouldn't hear it.