I can guess that they feel that having a high IQ posted on their resume, would give them some sort of an advantage in the job they are applying for.
However, I’m wondering from the Interviewer’s perspective, if it makes them look desperate and perhaps vane?
I don’t have any hard evidence to back it up either way, only opinion. I certainly wouldn’t do it. But then again, I’m not a member of MENSA.
As originally answered on Quora.com