There is not much to learn, a monoid is a very simple abstraction.

Think for example about learning about the "iterator" abstraction. It's just something with "hasNext" and "next" operations, nothing more to understand. But when you know it you start seeing iterators everywhere, and you get frustrated when something that should be an iterator isn't so you cannot write a simple foreach loop. And you'll start implementing iterators in your own code, because you know that provides a lot of convenience for free to consumers.

Same thing for monoids. They're everywhere, they offer some convenience for free, and you'll be wondering why things that should have monoid instances don't.