Unity had a "Live Training" demo called Events: Creating a Simple Messaging System. This is often pointed to as an example of using the UnityEvent class that was introduced in Unity 4.6.
While this was a fun and educational video, it uses UnityEvents in a very odd way, wrapping them in a string-based notification system and hooking everything up in code. Honestly, you could have done exactly the same thing using standard C# events, and it wouldn't have made any difference. (Indeed, prior to UnityEvent, many Unity developers — myself included — did exactly that.)
So I decided to make my own video, accomplishing the same demo but using UnityEvent the way nature intended. The result is a lot less code, easier to maintain, and harder to screw up.