Airdrops are meant to gain traders of their altcoins, to encourage someone to register to their website, free advertisement to their platform by means of retweeting or sharing on social medias, to gain thousands of supporters or to enlarge their social community on slack, discord or telegram, etc. Actually, that airdrop is an eye catcher to cryptocurrency's freelancers which as known as bounty hunters.
It's really help project become popular and bring more invest join their ICO, but not all of them success, actually I need to said that most of them failed, I think there are a lot of project come out right now, include scam ICO, 100 airdrop below 5 project will become success, so I'm already lazy to join airdrop program