For some time I was also interested in the subject of airdrop and even participated a couple of times. But the main disadvantage of such shares, the user receives a minimum of tokens, which he then most often cannot sell for a long time. This devalues tokens.
Free tokens always attract hunters. This gives an increase in the awareness of the project, however, I would not consider airdrop as the best way to promote ICO. Many users come, but the project has no value for them, they are only looking for a way to get tokens for free and then sell them