Cross-posting within the StackExchange network like that is generally frowned upon, although Unity Answers is not actually part of the StackExchange network (it just uses similar software).
I would still argue, however, that by cross-posting you devalue both communities slightly because you split the answer pool and don't provide that single authoritative answer.
Consequently, I'd apply a similar rule to that which is applied to determine if a question is better here or on SO - would a dedicated Unity developer be able to give you a better answer than a general game developer? If so, post on Unity Answers. Otherwise post here.
This means if you are asking how to do something specific to Unity, I'd say you should put it over there. But if you are asking how to do something that just happens to use Unity but isn't really about twiddling any particular knobs and dials Unity provides, or directly using Unity's APIs, ask it here.
Optimally, any of the Unity experts that hang out here would also be hanging out there, so you aren't going to narrow your audience that much by posting to a single site. (I cannot confirm this hypothesis of course, since I don't have analysis tools at Unity Answers.)
