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!
I havent join any airdrops yet but Ive heard a lot of bad news about it. Many crypto users are against it because most of it are scams according to them and they think it is just a waste of time. But of course it would be worth it if they get to earn from it specially for free.