Questions are often, maybe even typically, the triggers for an outstanding discussion. And bear in mind, a new member is often going to be a bit intimidated either in commenting (who am I to be chiming in along with these people with thousands of posts each?) or questioning (won't people laugh at me or get impatient for asking something that's probably so obvious/well-known/trivial/etc?) So repping a new member's useful question is a way (and a powerful one, I believe) to encourage them: yes, that's exactly what we're hoping for from you on MT, keep up the good work, etc. Actually, in some ways it's the most effective use of the rep system, I think.