I'm sure this has been debated in other threads but I wanted to highlight it.
This isn't so much a question of "when should Superman intervene in human history" but rather asking creative ways in which Superman should help advance humanity, whether morally, scientifically, intellectually, or otherwise.
We all know he primarily does it by example, acting in ways that inspire humans to act similarly. But what societal gifts can he give that only he can provide? He is the Man of Tomorrow after all; what instruments from the promise of a better future does he pass on?
Some examples:
-Using his senses to develop new theories of thermodynamics & renewable energy production and engineering
-Regularly providing information and materials from space for us to learn from
-Occasionally dropping in on medical professionals to help cure a medical epidemic or precarious surgical procedure
-Giving Ted-Talk like lectures at Universities on sociological analysis (though I can see Wonder Woman doing this more often)
-Occasionally helping elite musicians discover new sounds and arrangements for fun
Ideally I see the whole league doing these like this, advancing science and medicine and philosophy and economics and art when not saving the world from natural disaster and bad guys, but Superman is uniquely positioned to operate on a lot of fronts with the trust of the world.
So what would you like to see?