Unless I missed it-- I'm a bit suprised nobody here mentioned how complex the Enneagram is. It's nine main types, but when you add wings and instinctual variants, there are hundreds of types... and then levels of integration/health on top of that. It's very nuanced. You've got to study it a bit to really understand it, not just take a basic test. Same goes for any personality system.
Finding out that I was a four changed my life. I realized, oh, here are my behavior patterns, here is why I get along so well with some people and not with others. It was the first time I realized (perhaps this a symptom of my four narcissicm, ha) that not everyone sees the world the same way... not everyone sees the world MY way... therefore it is effective to try and learn about everyone's different paradigms. When I began to figure out others' types, I understood more how to relate to them, what worked and what didn't. Even if THEY aren't into the Enneagram, it's helpful for me to know their basic type to understand how I can be around them in the best way. For instance, my mom doesn't give a crap about the Enneagram, but since I know she is a nine, our relationship's become so much better-- I understand now that she shuts down when I am "overly" emotional. So I come at her from a different angle than if she were another four, or another emotional type, or whatnot.
The problem is when the Ennegram becomes a dogma instead of just a set of skillful tools and frames. But this is a problem with any system, MBTI included. They're all just useful ways of framing personality so that we can understand how to more effectively move through the world.