This was a question from @photonerddan during class, and after looking through many examples online approaching it from an inheritance stance, as well as ones with examples that seemed outside of common use-cases, Mike and I decided to approach it from a problem / solution standpoint, which looks at it from a database perspective.
We will cover it more in-depth during the second week of Rails MakerSquare, but for now here is a short example to highlight the problem that polymorphism is solving in your database.
So let's start with the problem it is solving:
Polymorphism keeps you from having excessive foreign key columns in a database table where multiple things, such as notification feed items, are owned by other objects.