It's just a saying I heard a long time ago from one of my professors. He probably meant it in the academic sense, i.e. the person could otherwise use that mental energy to do great research.

This point of view is understandable coming from a scientist, but essentially he could've said the same about van Beethoven or Dostoyevsky :)

Their works please us - not unlike the greatest chess games - but do they broaden our knowledge?

And where lies the value of great research anyway? In its practical appliance?

Grigori Perelman's research on the Poincaré conjecture is beyond brilliant, but has it improved our life more than the Immortal Game (Anderssen - Kieseritzky)?

Or is there innate value in scientific research, which comes solely from the virtue of being scientific? This approach strikes me as para-religious.

Refutation of the Evans gambit is some sort of knowledge as well. It's even peer reviewed :)

Of course it's not useful, but, for instance, is knowing what god was worshipped by the Khori-Tumed tribe 1200 years ago (fruit of hard and deep historical research work as it might be) more useful?