In any classification (of anything), one must have enough categories to account for most of the differences, but not so many categories that the classifications become useless. Meyers Briggs has 16, which is four more than basic astrology, but certainly small enough to handle.
I was delighted when I discovered (in my twenties) that your sun sign is only a small part of the story. Maybe the largest influence, but maybe not. Me, I am a double libra with a saggitarius moon. [I think I have like one planet in earth, everything in my chart is air)(libra is cardinal air, the airiest of air, and I have two of 'em] I announced this to a new age therapy/worker I had just met (in the middle of a session) and she pronounced, 'oh, that's why you're so mouthy.' I laughed (and, discounted most of the rest of what she said) because I had a very comfortable degree of certainty that NO one who knew me would ever use the adjective 'mouthy' to describe ME.
But when I was reading the Libra book that told of all the combinations with moons and risings that the description of me was far more accurate than any simple sun sign description I had ever read.
(yah, opalescent, experimenting!
I am very fond of Breszny's fr33will astrology, as it's far more imaginative and provides more useful things to think about than most common presentations of astrology.