I used to be obsessed with MBTI, on all the relevant forums, reading up on related personality theories (socionics, enneagram, OCEAN/Big 5, etc.) It was fun stuff. It's very pseudo-sciencey and there are a lot of people online that will be like "oh, I'm an ESTP and you said you're an INFP so I'm going to make you cry and we're bound to hate each other," when life is usually not like that at all, but just reading about these things make you think about yourself and what you like and how you think and all that and it can be very insightful if you use personality theory as a tool the right way.