Scaling without revenue makes sense if you're in an industry with strong network externalities or large economies of scale. In those cases, expensive customer acquisition is okay because customers have a very high lifetime value.

During the "unicorn boom", I think we all had this belief that network externalities were very common in tech - a belief driven by the rise of facebook, google, and others. But now we're realizing that maybe strong network externalities are just as rare in tech as they are in other industries - and a business without network effects that's losing money for growth is just a business that loses a lot of money.

This NYT article from last week seemed to do a good job summing up the issue: http://www.nytimes.com/2016/02/13/business/dealbook/the-rise...