It's obvious why one should vote on answers:
However, it's less obvious why one should vote on questions. Why should one vote on questions?
I don't know what others do, but on Stack Overflow:
Basically, it's my way to thank the asker for bringing me the answers I needed before I knew I needed them.
For example, I also used to have this question ― thus, +1 for you.
I upvote a lot of questions, especially if I'm interested in learning the answer myself. If it's important enough for me to favorite, even if for only a day, it gets my upvote.
I also upvote old questions if they contained an answer I was searching for. It's a small way of saying Thanks for asking first and saving me some time.
I don't downvote much at all, really, except in cases where people are blatantly rude. In those cases, a flag or a vote to close is more effective than a downvote anyway.
Rewards are important when you want to stimulate a certain behavior.
That's why I upvote.
Because it gives postive feedback that you think that it is either a great question. I up vote questions that made me think, even if at first glance it seems a simple subject. Or because no matter what level the question actually is, it is obvious that the asker actually took the time to think about it and shows both their own investigation and clearly states what the question is.
Voting down when it is obvious the person hasn't even taken the time to google for an answer. If the question is badly phrased, leave a comment asking for more information / clarification 1st and possibly only mark down if there is no response / edit.
Simple algorithm: If a question is worth my time writing an answer for, it's worth an upvote.
Though in general voting is for posts, not for users, voting actually also feeds the Sorry, we are no longer accepting questions from this account, to filter out low quality questions.
If you don't make a regular habit of downvoting awful questions, you just accumulate more and more rep. And then you have to build a room to keep it in, and hire a ninja to guard it, worry about it all the time. Far better to spend it by feeding the "Sorry, we are no longer accepting questions from this account" machinery.
