Like, how long I hesitated before I picked up something, what I had already in my "cart" at the time, what deals I looked at but passed on, etc.
While we are covering your high blood pressure medication?
Well, I guess we'll just increase your rates then...
I'm not sure it buys them anything, though. That's a very noisy signal against the loud-and-clear signal of what the measurements say when you come in to the doctor. Who cares what your shopping habits say when you come in with high blood pressure and morbid obesity, or good blood pressure and normal weight?
The change is specifically in in-store behavior. And even that's more because Amazon has the money and skillset to fund the software; the supermarkets already have the data in the sense that they have the video streams, they just don't have the money to fund people running beyond-cutting-edge vision research on it to get that level of analysis.