its just a massive pyramid scheme. everybody goes there to vote, and roll the dice on getting the #1 tag for fake social proof. its useful for social proof insofar as the vast majority of people dont know that product hunt is fake.
semi related fun fact, i had a friend run the numbers for fun - 8% of "#1 of the day" winners die within a year of launch https://twitter.com/jakobgreenfeld/status/146816583831853875...