If you give out a bounty immediately it seems potential abuse of the rep system where you could just rapidly dump rep to another user. If this is related to OMG, it's the HOLIDAY BOUNTY GIVEAWAY, I don't really care much for the whole pre-meditated bounty thing as people can just up-vote.
In any case, the "proper" use case of the bounty is to draw some additional eyes to a question, and as everyone is not always on (people sleep believe it or not), give other people a fair chance to craft a bounty-worthy answer. There may be a good answer now, but there could also be a great answer if you wait some hours.