I don't think airdrops are meant for investors but in a way it affects the success of a project, its purely for marketing purposes I think. The more noise a project will make the more it would likely to succeed, that's why they airdrop some of the tokens in replace of likes and shares from their project's social media pages. Some of the project's I know didn't airdrop their token but still have been successful, namely menlo and OPP.