QnA sites are just for outreach just like this forum. They will not help you in getting any rank better.

No, Q & A sites no longer help in site ranking because each one gives no-follow links, which help only in traffic.

We don't use Q&As solely for rankings but they do generate traffic. Can't always be predicted though. Quora is the largest, you'll find almost any topic in any niche.

Thanks for your responses. I am using Quora only to generate some traffic.