Question in the title. To think about, there are some fields in which having a very high IQ does not give someone any more advantage over someone with only a moderately high IQ. Some fields off the top of my head would be things like nursing, counseling, wildlife biology, etc. I'm not saying being smart isn't an advantage in those fields, but having a genius intellect is not going to help one any more than having a moderately high intellect.
So, what fields allow someone with a very high intellect (let's say 150 IQ or greater) to fully use their mind and continually be challenged? Math? Writing? Engineering?