When startup holds its own airdrop it works like a sort of avertisment. People get free coins and they get interested in it, especially if it gets some value in $.
This.
If you can pull off the airdrop well enough you'll be attracting more people. Nowadays there are a lot of crappy airdrops so what's important is to stand out.
If you manage to do that, go for it. Additionally, you can do both, airdrops and campaigns.