I have the impression that the preferred style of questions on StackOverflow is about problems which are very concrete, pragmatic, and well-defined. Which is fine — those criteria can help focus discussions.
But at the same time, Julia is a language that is breaking new ground and exploring novel ideas and concepts all the time. While the “core” language is more or less settled now (for 1.x), best practices are still evolving, new ideas are experimented with, and hypothetical discussion or speculative requests for advice are always welcome on this forum.
Also, a lot of contributors here have a pedagogical approach and pay attention to writing clean code, being ready to explain why something was done in a particular way. Even reading discussions here I don’t directly participate in is very educational.
Moreover, since there are a lot of domain experts hanging around, it is not unusual to receive great advice on linear algebra, statistics and probability, differential equations, optimization, and a lot of other topics which are not strictly about the language or its libraries, and would be very likely to be marked off-topic on SO. Amazingly, this while a lot of this is off-topic it is mostly self-regulated by polite people so it does not get out of hand.
So after doing some research (to avoid asking trivial questions if possible), I always just ask questions here and don’t even consider SO.