Yep, this is more the freemium model part.. https://en.wikipedia.org/wiki/Freemium On Thu, 26 Feb 2015, Ryan Carboni wrote:

The marginal cost of providing an additional account to the average user is pretty cheap. It is my understanding that the business models of most "cloud" companies is to provide a little free service to get users accustomed to their UIs, so that they would purchase a business license or equivalent.

Dropbox does not make it's money through data mining or advertising. Correct me if I'm wrong.