The assumption behind these tests is that the distribution along a line like "extrovert" and "introvert" is bipolar, that most people are either one or the other. The studies I've seen refute that, and if extrovert/introvert is even a valid concept, there is a normal distribution rather than a bipolar one. In other words, the median person is neither extroverted nor introverted but a little of both and that more people are near the middle of the range than the ends.
As for whether it's a valid concept at all, there's also reason to think OTHER FACTORS explain most of what people think of as "introvert" or "extrovert" behavior, and these factors may not even cluster. So, for example, whether you like being the center of attention may have nothing to do with whether being around other people energizes you, whether you enjoy speaking to a room may be totally unrelated to your being a charismatic outgoing conversationalist. And so on. There is a social assumption and cultural belief that these things cluster together and that there are "introverts" and "extroverts", but there isn't a whole heck of a lot of actual scientific data to support that belief -- other than some dodgy studies published by people who profit from selling products based on Meyers Briggs.
I have also noticed that my results changed as my career changed. Early in my career when I was focused on being an individual contributor in my organization, beavering away on my own work, I scored more highly on the introverted thinker stuff. When I increasingly moved into management rolls I started scoring higher on other factors, moving more towards the E side.
I don't that at some level it was a good description of how I was behaving at that time in my life BUT the M-B claim is you should use this stuff to find out what job is best suited to you. I'm inclined to believe it's the other way around--the job you're currently doing influences how you score on this test. As in, whatever skills and behaviors are prioritized by your current employment are going to be things you decide to exhibit and emphasize in your behaviors -- that your employment choices determine your M-B categorization, and not the other way around. The implication being that you shouldn't change careers because of your M-B scores, on the contrary, your scores will change if you change careers.
TLDR; you find M-B discussed primarily in pop business books, and hardly ever discussed in serious social science journals