Q:

When should we ask questions on Reddit?

I recently involve more in Reddit, and surprisingly find out a subreddit named AskAcademia. I know that Stack Exchange is not Reddit, and the way Reddit works is different to the way SE works. In SE, people ask and answer. In Reddit, people post a link/thinking and comment. However, in Q&A subreddit like AskAcademia, I see no different to here. Bad questions may never be closed, but they will never be raised. Can you tell me when should I ask questions on Reddit rather than Stack Exchange? 

A:

You should ask a question on Reddit whenever you feel like it, regardless of whether you ask the question on Academia.SE.
Academia.SE doesn't make any claim to be the only site you should ask a question on.  It only asks that you not ask the same question on any other SE site, because that is general SE policy.

A:

Reddit

Born for open-ended discussions
After 6 months posts are automatically locked so discussions are "fossilized" to reflect what happened in that time
No way for users to improve others' posts
Downvotes can (and usually?) mean "I don't like this" or "this is uninteresting"
The only way to have links to relevant posts within the subreddit is by having other users provide
More active users in my opinion

Stack Exchange

Born for Q&A
Posts can always be improved until the Sun dies
Contributions from users are encouraged and peer-reviewed
Downvotes mean "This post is wrong/not useful"
Have tag system, related questions to categorize and discover more questions/answers
Posts can have images, HTML. The site overall is nicely designed

