The time to complete an airdrop is very short. I don't think this is a waste of time because some airdrops still allow us to get a small amount of revenue. On the contrary, some bounty tasks that will take weeks or months to complete will eventually disappear. This is the most time-wasting thing!
Do not forget the important point... And what do you do with those coins you got from the air drops. Well, they're on your wallet and then? To bring them to the exchange, you have the minimum breeds to sell. You have to buy some coins to sell everything at once.... Therefore, this is not always the best option in contrast to the bounty.