Actually airdrops are made to collect free tocken of the coin before to launch , it doesn't mean that you will get in unlimited amount but you will get small free amount of tocken and you can buy also in any amount . And also you can make free by sharing your referral link and in this way you can make free coins in better amount but you will needed to share your referral link with your friends and at most of the possibility to platforms where you can make better amount of money if ICO get successful .
Airdrop is a type of the referral system which helps to the team of the ICOs to get more numbers of the investors easily to invest in Thier ICO .