I've seen a few bounty campaigns in my days. Quite a business model, I tell you, fits in just great with the ICO. It's a great way to start off a successful ICO campaign.
But many dev teams start their ICO without a bounty. The bounty launches several weeks or months later just to make the project more popular. Remember that the bounty requires some investments from devs too.
Of course, bounty campaign requires periodical time investments on dev's part, but I've seen how much attention such campaign could bring. Human resources are much more valuable than time, don't forget that!
Exactly! Huge amount of reposts/retweets can promote company as well as satisfy people's lust for money, that's the way how bounty campaign works!