What is something that you’re expert in but doesn’t propel you professionally at all?

I’m using the term “expert” loosely here. Consider an area of great knowledge, skill and experience that simply gets left off of your resume because any connection to your advancement professionally might be considered ridiculous.
Do you have an area of expertise that is based entirely off of your personal affinity for the subject matter?
What is something that you’re expert in but doesn’t propel you professionally at all?
What is something that you’re expert in but doesn’t propel you professionally at all?
What is something that you’re expert in but doesn’t propel you professionally at all?
Post Opinion