Yes but now there is a record of every single thing you've ever bought. Of course for most people this probably doesn't matter too much. But some people do value privacy.
You could go half-way and leak a very biased sample of data. Some people are terrified that there might come a day where our health insurers monitor the junk food we buy via our credit card purchases. But why not just buy junk food with cash and healthy food with a credit card.
