You don't need it, cause you've got StackOverflow and GitHub to build your rep, leaving aside the 'just launch' of putting your own technical talent out there.
If you're not in a tech field, say as a screenwriter in Hollywood—excellent Quora use case, btw—it's a great way to build your brand and increase your chances of discovery/personal breakout. Quora helped me launch my career, working with Startup Visa. It's gotten me political meetings and was warmly received as I'm applying for a fellowship.
Quora's a publishing platform with an increasing number of ways to get into publications. Right now, the two big ones are Forbes, Huffington Post, but I'm sure they're expanding in that direction, based on the utter awesomeness of their weekly and daily digests in contrast with the eh launches of most of their technical additions, from credits on to views.
As a political person, I love it, definitely the best place for thoughtful, civil political discussion on the web, even if that has its failure modes.