From what I can tell, school admissions "classify" people based on a few categories: ethnicity, citizenship, employers, university history/degrees, and career interests. The adcom is looking for diversity across all of those and depending on the admissions officer, you can get grouped into a pool in any one of those areas.
A good gauge to see what a "typical" applicant or student at a school looks like, would be the class profile. Many times it'll show the college majors and professional background of students in their newest class. From what I've seen, there's a lot of people from consulting, finance, banking, accounting, and engineering applying to business school. If you're an actuary I'm sure there's a few actuaries that have applied and some that will be applying.
I think there are pro's and con's of being from a "typical" b-school background. Admissions like people from certain employers and backgrounds with "typical" career goals because it is a
known variable. They know what to expect from the student and that their career goals are realistic (they are employable). The downside is that many people from the "typical" background are also highly qualified and ambitious and so if you get grouped in among them, it may be more difficult to stand out and impress the adcom.
Everyone's unique in their own way and you just have to make sure you aptly portray that to the adcom to help you stand out. It can be a hobby or a passion, or maybe even a unique travel experience. This is where the essays help people from a "generic" background.

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