Knowing your Meyers Briggs is a way of indicating traits, such as empathy, practical, feeling (or not terribly emotional). I put it there for those who recognize it. There is a book called "Please Understand Me, " which chronicles the MBTI and who you will be most attracted to - as well as whom you might want to avoid (even though you may be attracted to them).
It only works if the other person knows what you are likely to be like. I, for instance, and an INFJ. The INFJ could be akin, to, oh, say, Cassandra, a seeress in Greek mythology, given her powers by Apollo - until she pissed him off and he altered them so she could only predict certain events (like the Trojan Horse debacle. She wasn't too popular after that one!) INFJ's abilities? Able to foresee past, present and future events, sense intention (both good and evil) in others and be the highly romantic type. But that would not a good match for say, an ESTJ, the used car salesman type - although that is who the INFJ might find appealing - for all the wrong reasons. I'd go for a nice ENFP and double that if he was short, Jewish, and hairy (hey, there has to be SOME sex appeal in this for me! Man cannot live by sainthood alone!) :lol
I'd imagine Steven Jobs was an ISTJ. Trump is likely an ESTJ/ESTP.
It is a fascinating branch of psychology. Wish more people knew about it. As to why one would put it on their profile? It's no different (for an INFJ) than saying you have a big heart, or you're the perceptive type. Of the expectations part? I don't put it there expecting anything. It's just a sort of shorthand for those who know it. Others will ignore it because they don't know what it means.