I know the implication is negative in terms of privacy, but it has its benefits if it could actually solve problems and provide value to the majority.
The problem is, though, that any form of bargaining (and sales is bargaining) is an information game. The more they know about you, the worse a deal you will get. One recent real example was the advertisers targeting women on their periods. Taking it further, imagine a liquor company finding out that you've just lost a family member and flooding you with ads for alcohol. The more they know about you, the worse you get screwed.