As the app mentioned is free, I would deduce that they try to turn the data about their users cycle into a monetary value. Is there research how certain periods of the cycle would affect women shopping behaviour (or behaviour in general)? I am asking this to understand how much value is in such information. Perhaps there are other aspects I am overlooking?
There are good reasons why people might want to make this sort of app beyond selling the data. There's a huge potential for health care service providers - if women don't need prescription drugs or appointments to see their doctor, and any other medical issues are resolved more easily because there isn't the problem of the drugs interacting with the pill, then that represents a vast saving in the cost of supplying services.