I think that airdrops can have a positive marketing value, if dropped in small amounts per person. Enough so that the receiver is curious about the coin and wants to learn more about it. If it's a small amount there is no benefit to trying to run to the market with it, but if you research the coin and decide it has potential there is every reason to keep it. Maybe even invest more in to it. I received a large airdrop of Stellar Lumens around the end of 2017 when the market was booming. It was over $4,000 worth! I sold them, because it was a large amount and I didn't know anything about XLM, I just took the money and invested it in Bitcoin. But I have received small amounts of other coins, that I have looked into and kept. I do not think it profitable for the company or the early investors to give away large amounts to individual. It only crashes the market.