I am afraid bounties are coming into this category as well. FOr all the popular ICOs now there are no bounties
You can see Beetoken for example.
the airdrop for me its super profitable to gained money, even its all free but you need also to support them, what i mean is if you buy some token or coin for better,. i know they dont yet if they success the project i just suggest its get to support them, even its small money you spend in that project but soon your spend money to his project your profit make 3x income.
It is sad to say that freedrops coins are mostly no value in the market today. Previously a lot of people are joining this because it seems to be a sort of extra income and the good thing is that which is free. But, when cryptocurrency begun to spread, fake coins are started to spread that it only makes people to be fooled. That's the reason why I just ignore and never participated on this.