I also agree with you. Airdrop is a kind of giveaway that is used as a means of promotion, Airdrop participants are usually required to perform certain tasks as a condition for obtaining a number of Cryptocurrency Tokens. But nowadays most of the Airdrops are scams and we should careful. I also signed up several airdrops past 2 weeks and i got tokens only from one airdrop. So it is a waste of our time and it is not easy to get a profit out of it.
You are on right track, In beginner stage most of the people will do this mistakes by signing up for all airdrops what they come across. There are many potential airdrops happening around. Instead of simply sign up, spend some time for each airdrop and find the best.
And don't forget - Once you became pro in finding best, share your knowledge to the community.