Cryptocurrecy bounties, airdrops and exchange talk are important for the development and support of these cryptos. The importance of them cannot be overly emphasized on. They are needed to promote new ICOs, or already existing ones. They have also proven to be a way that people who are interested in it can make good earnings.
They have also proven to be an easy way to trick crypto investors and pump and dump cryptocurrency. They are not necessarily needed. If something is truly valuable, one doesn't give it away so easily. In the case of bounties, it's paid marketing, but the bounty hunters more often than not dump the coins/tokens for bitcoin and ether as soon as they get listed on exchanges.