What is the use of user data collection besides serving ads?
A couple of days ago developers from one product company asked me how they can understand why new users were leaving their website. My first question to them was what these users' profiles looked like and how they were different from those who stayed. 

Advertising is only top of an iceberg. User profiles (either filled by users themselves or computed from users' behaviour) hold information about: 


user categories, i.e. what kind of people tend to use your website/product
paying client portraits, i.e. who is more likely to use your paid services
UX component performance, e.g. how long it takes people to find the button they need
action performance comparison, e.g. what was more efficient - lower price for a weekend or propose gifts with each buy, etc. 


So it's more about improving product and making better user experience rather than selling this data to advertisers.