Assuming that advertising is going to be a primary source of revenue, than you aren't going to have much revenue to lose before you start advertising. The idea

Assuming that advertising is going to be a primary source of revenue, than you aren't going to have much revenue to lose before you start advertising. The idea is that companies don't advertise at first to take advantage of the exponential growth and user retention when they start getting hot, and once they have market share they start to target profit rather than growth.