Airdrop can be worth it if you really invest on the same coin/token, because we know that its not a big amount.
It looks like you missed to read the posts above yours.
It is not about how much free coins you receive from airdrop but the concern here is whether those coins are really worth or not and got any future use of those coins. If no use of those coins and team behind those coins are series in bringing up the product then those coins eventually become a shit coin and you lose all your invested money. So better get all the information about the coin before you invest your hard-earned money.