In response to Veale's request, Netflix disclosed that it uses an individual's choices to figure out which segment of the story to serve up. That makes sense, of course. Were a person to step away from Bandersnatch in the middle of the story, Netflix would be able to remember the path they took and serve up the correct story branches.
Netflix also aggregates all of the choices made by users to see how audiences as a whole are interacting with the story. The company told Veale in an email that information is used to "determine how to improve this model of storytelling in the context of a show or movie." Netflix didn't reveal how long it stores data relating to people's decisions.
It's probably not a major surprise that Netflix has stashed away all sorts of data about how people interacted with Bandersnatch. It was the company's first crack at a choose-your-own-adventure story and the information gathered from it will likely help Netflix decide if it's worth telling more stories through that format. However, it serves as a good reminder that companies collect just about every bit of information they can from you, including seemingly innocuous data points, and hold onto that information indefinitely without explicit consent to do so.